Brings the MDC skiplist optimizations from develop

10 files changed, 2305 insertions, 787 deletions

diff --git a/src/H5AC.c b/src/H5AC.c
index 2b9a410..a8de8ea 100644
--- a/src/H5AC.c
+++ b/src/H5AC.c
@@ -140,8 +140,8 @@ static const H5AC_class_t *const H5AC_class_s[] = {
  *
  * Purpose:     Initialize the interface from some other layer.
  *
- * Return:      Success:    non-negative
- *              Failure:    negative
+ * Return:      Success:        non-negative
+ *              Failure:        negative
  *
  * Programmer:  Quincey Koziol
  *              Saturday, January 18, 2003
@@ -162,7 +162,7 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function     H5AC__init_package
+ * Function:    H5AC__init_package
  *
  * Purpose:     Initialize interface-specific information
  *
@@ -202,9 +202,9 @@ H5AC__init_package(void)
  *
  * Purpose:     Terminate this interface.
  *
- * Return:      Success:    Positive if anything was done that might
- *                affect other interfaces; zero otherwise.
- *              Failure:    Negative.
+ * Return:      Success:        Positive if anything was done that might
+ *                              affect other interfaces; zero otherwise.
+ *              Failure:        Negative.
  *
  * Programmer:  Quincey Koziol
  *              Thursday, July 18, 2002
@@ -281,7 +281,7 @@ herr_t
 H5AC_create(const H5F_t *f, H5AC_cache_config_t *config_ptr, H5AC_cache_image_config_t * image_config_ptr)
 {
 #ifdef H5_HAVE_PARALLEL
-    char      prefix[H5C__PREFIX_LEN] = "";
+    char         prefix[H5C__PREFIX_LEN] = "";
     H5AC_aux_t * aux_ptr = NULL;
 #endif /* H5_HAVE_PARALLEL */
     struct H5C_cache_image_ctl_t int_ci_config = H5C__DEFAULT_CACHE_IMAGE_CTL;
@@ -468,6 +468,14 @@ done:
  * Programmer:  Robb Matzke
  *              Jul  9 1997
  *
+ * Changes:
+ *
+ *             In the parallel case, added code to setup the MDC slist 
+ *             before the call to H5AC__flush_entries() and take it down
+ *             afterwards.  
+ *             
+ *                                            JRM -- 7/29/20
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
@@ -493,58 +501,115 @@ H5AC_dest(H5F_t *f)
 #endif /* H5AC_DUMP_STATS_ON_CLOSE */
 
     /* Check if log messages are being emitted */
-    if(H5C_get_logging_status(f->shared->cache, &log_enabled, &curr_logging) < 0)
+    if(H5C_get_logging_status(f->shared->cache, 
+                              &log_enabled, &curr_logging) < 0)
+
         HGOTO_ERROR(H5E_CACHE, H5E_LOGGING, FAIL, "unable to get logging status")
-    if(log_enabled && curr_logging)
+    if(log_enabled && curr_logging) {
+
         if(H5C_log_write_destroy_cache_msg(f->shared->cache) < 0)
-            HDONE_ERROR(H5E_CACHE, H5E_LOGGING, FAIL, "unable to emit log message")
+
+            HDONE_ERROR(H5E_CACHE, H5E_LOGGING, FAIL, \
+                        "unable to emit log message")
+    }
+
     /* Tear down logging */
-    if(log_enabled)
+    if(log_enabled) {
+
         if(H5C_log_tear_down(f->shared->cache) < 0)
-            HGOTO_ERROR(H5E_CACHE, H5E_LOGGING, FAIL, "mdc logging tear-down failed")
+
+            HGOTO_ERROR(H5E_CACHE, H5E_LOGGING, FAIL, \
+                        "mdc logging tear-down failed")
+    }
 
 #ifdef H5_HAVE_PARALLEL
+
     /* destroying the cache, so clear all collective entries */
     if(H5C_clear_coll_entries(f->shared->cache, FALSE) < 0)
-        HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "H5C_clear_coll_entries() failed")
+
+        HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, \
+                    "H5C_clear_coll_entries() failed")
 
     aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(f->shared->cache);
-    if(aux_ptr)
+
+    if(aux_ptr) {
+
         /* Sanity check */
         HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
+    
+
+        /* If the file was opened R/W, attempt to flush all entries
+         * from rank 0 & Bcast clean list to other ranks.
+         *
+         * Must not flush in the R/O case, as this will trigger the
+         * free space manager settle routines.
+         *
+         * Must also enable the skip list before the call to 
+         * H5AC__flush_entries() and disable it afterwards, as the 
+         * skip list will be disabled after the previous flush.
+         *
+         * Note that H5C_dest() does slist setup and take down as well.
+         * Unfortunately, we can't do the setup and take down just once,
+         * as H5C_dest() is called directly in the test code.
+         *
+         * Fortunately, the cache should be clean or close to it at this
+         * point, so the overhead should be minimal.
+         */
+        if(H5F_ACC_RDWR & H5F_INTENT(f)) {
 
-    /* If the file was opened R/W, attempt to flush all entries
-     * from rank 0 & Bcast clean list to other ranks.
-     *
-     * Must not flush in the R/O case, as this will trigger the
-     * free space manager settle routines.
-     */
-    if(H5F_ACC_RDWR & H5F_INTENT(f))
-        if(H5AC__flush_entries(f) < 0)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't flush")
+            /* enable and load the slist */
+            if ( H5C_set_slist_enabled(f->shared->cache, TRUE, FALSE) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                            "set slist enabled failed")
+
+            if(H5AC__flush_entries(f) < 0)
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't flush")
+
+            /* disable the slist -- should be empty */
+            if ( H5C_set_slist_enabled(f->shared->cache, FALSE, FALSE) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "disable slist failed")
+        }
+    }
 #endif /* H5_HAVE_PARALLEL */
 
     /* Destroy the cache */
     if(H5C_dest(f) < 0)
+
         HGOTO_ERROR(H5E_CACHE, H5E_CANTFREE, FAIL, "can't destroy cache")
+
     f->shared->cache = NULL;
 
 #ifdef H5_HAVE_PARALLEL
+
     if(aux_ptr != NULL) {
+
         if(aux_ptr->d_slist_ptr != NULL) {
+
             HDassert(H5SL_count(aux_ptr->d_slist_ptr) == 0);
             H5SL_close(aux_ptr->d_slist_ptr);
+
         } /* end if */
+
         if(aux_ptr->c_slist_ptr != NULL) {
+
             HDassert(H5SL_count(aux_ptr->c_slist_ptr) == 0);
             H5SL_close(aux_ptr->c_slist_ptr);
+
         } /* end if */
+
         if(aux_ptr->candidate_slist_ptr != NULL) {
+
             HDassert(H5SL_count(aux_ptr->candidate_slist_ptr) == 0);
             H5SL_close(aux_ptr->candidate_slist_ptr);
+
         } /* end if */
+
         aux_ptr->magic = 0;
         aux_ptr = H5FL_FREE(H5AC_aux_t, aux_ptr);
+
     } /* end if */
 #endif /* H5_HAVE_PARALLEL */
 
@@ -776,20 +841,20 @@ H5AC_get_entry_status(const H5F_t *f, haddr_t addr, unsigned *status)
 
     if(in_cache) {
         *status |= H5AC_ES__IN_CACHE;
-    if(is_dirty)
-        *status |= H5AC_ES__IS_DIRTY;
-    if(is_protected)
-        *status |= H5AC_ES__IS_PROTECTED;
-    if(is_pinned)
-        *status |= H5AC_ES__IS_PINNED;
-    if(is_corked)
-        *status |= H5AC_ES__IS_CORKED;
-    if(is_flush_dep_parent)
-        *status |= H5AC_ES__IS_FLUSH_DEP_PARENT;
-    if(is_flush_dep_child)
-        *status |= H5AC_ES__IS_FLUSH_DEP_CHILD;
-    if(image_is_up_to_date)
-        *status |= H5AC_ES__IMAGE_IS_UP_TO_DATE;
+        if(is_dirty)
+            *status |= H5AC_ES__IS_DIRTY;
+        if(is_protected)
+            *status |= H5AC_ES__IS_PROTECTED;
+        if(is_pinned)
+            *status |= H5AC_ES__IS_PINNED;
+        if(is_corked)
+            *status |= H5AC_ES__IS_CORKED;
+        if(is_flush_dep_parent)
+            *status |= H5AC_ES__IS_FLUSH_DEP_PARENT;
+        if(is_flush_dep_child)
+            *status |= H5AC_ES__IS_FLUSH_DEP_CHILD;
+        if(image_is_up_to_date)
+            *status |= H5AC_ES__IMAGE_IS_UP_TO_DATE;
     } /* end if */
     else
         *status = 0;
@@ -1240,6 +1305,109 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ *
+ * Function:    H5AC_prep_for_file_flush
+ *
+ * Purpose:     This function should be called just prior to the first 
+ *              call to H5AC_flush() during a file flush.
+ *
+ *              Its purpose is to handly any setup required prior to 
+ *              metadata cache flush.  
+ *
+ *              Initially, this means setting up the slist prior to the
+ *              flush.  We do this in a seperate call because 
+ *              H5F__flush_phase2() make repeated calls to H5AC_flush().
+ *              Handling this detail in separate calls allows us to avoid 
+ *              the overhead of setting up and taking down the skip list 
+ *              repeatedly.
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  John Mainzer
+ *              5/5/20
+ *
+ * Changes:     None.
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5AC_prep_for_file_flush(H5F_t *f)
+{
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    /* Sanity checks */
+    HDassert(f);
+    HDassert(f->shared);
+    HDassert(f->shared->cache);
+
+    if ( H5C_set_slist_enabled(f->shared->cache, TRUE, FALSE) < 0)
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "slist enabled failed")
+
+done:
+
+    FUNC_LEAVE_NOAPI(ret_value)
+
+} /* H5AC_prep_for_file_flush() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function:    H5AC_secure_from_file_flush
+ *
+ * Purpose:     This function should be called just after the last 
+ *              call to H5AC_flush() during a file flush.
+ *
+ *              Its purpose is to perform any necessary cleanup after the
+ *              metadata cache flush.
+ *
+ *              The objective of the call is to allow the metadata cache
+ *              to do any necessary necessary cleanup work after a cache 
+ *              flush.
+ *
+ *              Initially, this means taking down the slist after the
+ *              flush.  We do this in a seperate call because 
+ *              H5F__flush_phase2() make repeated calls to H5AC_flush().
+ *              Handling this detail in separate calls allows us to avoid 
+ *              the overhead of setting up and taking down the skip list 
+ *              repeatedly.
+ *
+ * Return:      Non-negative on success/Negative on failure
+ *
+ * Programmer:  John Mainzer
+ *              5/5/20
+ *
+ * Changes:     None.
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5AC_secure_from_file_flush(H5F_t *f)
+{
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    /* Sanity checks */
+    HDassert(f);
+    HDassert(f->shared);
+    HDassert(f->shared->cache);
+
+    if ( H5C_set_slist_enabled(f->shared->cache, FALSE, FALSE) < 0)
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "slist enabled failed")
+
+done:
+
+    FUNC_LEAVE_NOAPI(ret_value)
+
+} /* H5AC_secure_from_file_flush() */
+
+
+/*-------------------------------------------------------------------------
+ *
  * Function:    H5AC_create_flush_dependency()
  *
  * Purpose:     Create a flush dependency between two entries in the metadata
@@ -1548,8 +1716,8 @@ herr_t
 H5AC_unprotect(H5F_t *f, const H5AC_class_t *type, haddr_t addr, void *thing,
     unsigned flags)
 {
-    hbool_t        dirtied;
-    hbool_t        deleted;
+    hbool_t             dirtied;
+    hbool_t             deleted;
 #ifdef H5_HAVE_PARALLEL
     H5AC_aux_t        * aux_ptr = NULL;
 #endif /* H5_HAVE_PARALLEL */
@@ -1570,14 +1738,14 @@ H5AC_unprotect(H5F_t *f, const H5AC_class_t *type, haddr_t addr, void *thing,
     HDassert(((H5AC_info_t *)thing)->type == type);
 
     dirtied = (hbool_t)(((flags & H5AC__DIRTIED_FLAG) == H5AC__DIRTIED_FLAG) ||
-        (((H5AC_info_t *)thing)->dirtied));
+                (((H5AC_info_t *)thing)->dirtied));
     deleted = (hbool_t)((flags & H5C__DELETED_FLAG) == H5C__DELETED_FLAG);
 
     /* Check if the size changed out from underneath us, if we're not deleting
      *  the entry.
      */
     if(dirtied && !deleted) {
-        size_t        curr_size = 0;
+        size_t          curr_size = 0;
 
         if((type->image_len)(thing, &curr_size) < 0)
             HGOTO_ERROR(H5E_CACHE, H5E_CANTGETSIZE, FAIL, "Can't get size of thing")
@@ -1664,7 +1832,7 @@ H5AC_get_cache_auto_resize_config(const H5AC_t *cache_ptr,
     if(internal_config.rpt_fcn == NULL)
         config_ptr->rpt_fcn_enabled = FALSE;
     else
-    config_ptr->rpt_fcn_enabled = TRUE;
+        config_ptr->rpt_fcn_enabled = TRUE;
     config_ptr->open_trace_file        = FALSE;
     config_ptr->close_trace_file       = FALSE;
     config_ptr->trace_file_name[0]     = '\0';
@@ -1926,7 +2094,7 @@ H5AC_validate_config(H5AC_cache_config_t *config_ptr)
 
     /* don't bother to test trace_file_name unless open_trace_file is TRUE */
     if(config_ptr->open_trace_file) {
-        size_t            name_len;
+        size_t           name_len;
 
         /* Can't really test the trace_file_name field without trying to
          * open the file, so we will content ourselves with a couple of
@@ -2047,9 +2215,9 @@ H5_ATTR_UNUSED
     *f, hbool_t *write_permitted_ptr)
 {
 #ifdef H5_HAVE_PARALLEL
-    H5AC_aux_t *    aux_ptr = NULL;
+    H5AC_aux_t *        aux_ptr = NULL;
 #endif /* H5_HAVE_PARALLEL */
-    hbool_t         write_permitted = TRUE;
+    hbool_t             write_permitted = TRUE;
 
     FUNC_ENTER_STATIC_NOERR
 
@@ -2546,8 +2714,8 @@ H5AC_set_ring(H5AC_ring_t ring, H5AC_ring_t *orig_ring)
  *              Note that this function simply passes the call on to
  *              the metadata cache proper, and returns the result.
  *
- * Return:      Success:    Non-negative
- *              Failure:    Negative
+ * Return:      Success:        Non-negative
+ *              Failure:        Negative
  *
  * Programmer:  Quincey Koziol
  *              September 17, 2016
@@ -2682,4 +2850,3 @@ H5AC_get_mdc_image_info(H5AC_t *cache_ptr, haddr_t *image_addr, hsize_t *image_l
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* H5AC_get_mdc_image_info() */
-
diff --git a/src/H5ACmpio.c b/src/H5ACmpio.c
index c6ffc80..7474460 100644
--- a/src/H5ACmpio.c
+++ b/src/H5ACmpio.c
@@ -791,7 +791,7 @@ H5AC__log_dirtied_entry(const H5AC_info_t *entry_ptr)
     else {
         aux_ptr->dirty_bytes += entry_ptr->size;
 #if H5AC_DEBUG_DIRTY_BYTES_CREATION
-        aux_ptr->unprotect_dirty_bytes += entry_size;
+        aux_ptr->unprotect_dirty_bytes += entry_ptr->size;
         aux_ptr->unprotect_dirty_bytes_updates += 1;
 #endif /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
     } /* end else */
@@ -989,7 +989,7 @@ H5AC__log_inserted_entry(const H5AC_info_t *entry_ptr)
     aux_ptr->dirty_bytes += entry_ptr->size;
 
 #if H5AC_DEBUG_DIRTY_BYTES_CREATION
-    aux_ptr->insert_dirty_bytes += size;
+    aux_ptr->insert_dirty_bytes += entry_ptr->size;
     aux_ptr->insert_dirty_bytes_updates += 1;
 #endif /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
 
@@ -1875,6 +1875,8 @@ done:
  * Programmer:  John Mainzer
  *              April 28, 2010
  *
+ * Changes:     None.
+ *
  *-------------------------------------------------------------------------
  */
 static herr_t
@@ -1894,7 +1896,8 @@ H5AC__rsp__p0_only__flush(H5F_t *f)
     aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
     HDassert(aux_ptr != NULL);
     HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
-    HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__PROCESS_0_ONLY);
+    HDassert(aux_ptr->metadata_write_strategy == \
+             H5AC_METADATA_WRITE_STRATEGY__PROCESS_0_ONLY);
 
     /* To prevent "messages from the future" we must
      * synchronize all processes before we start the flush.
@@ -1903,9 +1906,12 @@ H5AC__rsp__p0_only__flush(H5F_t *f)
      * However, when flushing from within the close operation from a file,
      * it's possible to skip this barrier (on the second flush of the cache).
      */
-    if(!H5CX_get_mpi_file_flushing())
-        if(MPI_SUCCESS != (mpi_result = MPI_Barrier(aux_ptr->mpi_comm)))
+    if ( ! H5CX_get_mpi_file_flushing() ) {
+
+        if ( MPI_SUCCESS != (mpi_result = MPI_Barrier(aux_ptr->mpi_comm)) )
+
             HMPI_GOTO_ERROR(FAIL, "MPI_Barrier failed", mpi_result)
+    }
 
     /* Flush data to disk, from rank 0 process */
     if(aux_ptr->mpi_rank == 0) {
@@ -1921,23 +1927,30 @@ H5AC__rsp__p0_only__flush(H5F_t *f)
         aux_ptr->write_permitted = FALSE;
 
         /* Check for error on the write operation */
-        if(result < 0)
+        if ( result < 0 )
+
             HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't flush.")
 
         /* this code exists primarily for the test bed -- it allows us to
          * enforce POSIX semantics on the server that pretends to be a
          * file system in our parallel tests.
          */
-        if(aux_ptr->write_done)
+        if ( aux_ptr->write_done ) {
+
             (aux_ptr->write_done)();
+        }
     } /* end if */
 
     /* Propagate cleaned entries to other ranks. */
-    if(H5AC__propagate_flushed_and_still_clean_entries_list(f) < 0)
-        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't propagate clean entries list.")
+    if ( H5AC__propagate_flushed_and_still_clean_entries_list(f) < 0 )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                    "Can't propagate clean entries list.")
 
 done:
+
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5AC__rsp__p0_only__flush() */
 
 
@@ -2104,16 +2117,22 @@ H5AC__run_sync_point(H5F_t *f, int sync_point_op)
 
     /* Sanity checks */
     HDassert(f != NULL);
+
     cache_ptr = f->shared->cache;
+
     HDassert(cache_ptr != NULL);
+
     aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
+
     HDassert(aux_ptr != NULL);
     HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
     HDassert((sync_point_op == H5AC_SYNC_POINT_OP__FLUSH_TO_MIN_CLEAN) ||
-        (sync_point_op == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED));
+             (sync_point_op == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED));
+
 
 #if H5AC_DEBUG_DIRTY_BYTES_CREATION
-HDfprintf(stdout, "%d:H5AC_propagate...:%u: (u/uu/i/iu/r/ru) = %zu/%u/%zu/%u/%zu/%u\n",
+HDfprintf(stdout, 
+    "%d:H5AC_propagate...:%u: (u/uu/i/iu/r/ru) = %zu/%u/%zu/%u/%zu/%u\n",
     aux_ptr->mpi_rank,
     aux_ptr->dirty_bytes_propagations,
     aux_ptr->unprotect_dirty_bytes,
@@ -2188,6 +2207,7 @@ HDfprintf(stdout, "%d:H5AC_propagate...:%u: (u/uu/i/iu/r/ru) = %zu/%u/%zu/%u/%zu
 #endif /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
 
 done:
+
     FUNC_LEAVE_NOAPI(ret_value)
 } /* H5AC__run_sync_point() */
 
diff --git a/src/H5ACprivate.h b/src/H5ACprivate.h
index 9f2c215..575c791 100644
--- a/src/H5ACprivate.h
+++ b/src/H5ACprivate.h
@@ -387,6 +387,8 @@ H5_DLL herr_t H5AC_insert_entry(H5F_t *f, const H5AC_class_t *type,
     haddr_t addr, void *thing, unsigned int flags);
 H5_DLL herr_t H5AC_pin_protected_entry(void *thing);
 H5_DLL herr_t H5AC_prep_for_file_close(H5F_t *f);
+H5_DLL herr_t H5AC_prep_for_file_flush(H5F_t *f);
+H5_DLL herr_t H5AC_secure_from_file_flush(H5F_t *f);
 H5_DLL herr_t H5AC_create_flush_dependency(void *parent_thing, void *child_thing);
 H5_DLL void * H5AC_protect(H5F_t *f, const H5AC_class_t *type, haddr_t addr,
     void *udata, unsigned flags);
diff --git a/src/H5C.c b/src/H5C.c
index f706a35..20182da 100644
--- a/src/H5C.c
+++ b/src/H5C.c
@@ -234,6 +234,82 @@ H5FL_BLK_DEFINE_STATIC(parent);
  * Programmer:  John Mainzer
  *              6/2/04
  *
+ * Modifications:
+ *
+ *              JRM -- 7/20/04
+ *              Updated for the addition of the hash table.
+ *
+ *              JRM -- 10/5/04
+ *              Added call to H5C_reset_cache_hit_rate_stats().  Also
+ *              added initialization for cache_is_full flag and for
+ *              resize_ctl.
+ *
+ *              JRM -- 11/12/04
+ *              Added initialization for the new size_decreased field.
+ *
+ *              JRM -- 11/17/04
+ *              Added/updated initialization for the automatic cache
+ *              size control data structures.
+ *
+ *              JRM -- 6/24/05
+ *              Added support for the new write_permitted field of
+ *              the H5C_t structure.
+ *
+ *              JRM -- 7/5/05
+ *              Added the new log_flush parameter and supporting code.
+ *
+ *              JRM -- 9/21/05
+ *              Added the new aux_ptr parameter and supporting code.
+ *
+ *              JRM -- 1/20/06
+ *              Added initialization of the new prefix field in H5C_t.
+ *
+ *              JRM -- 3/16/06
+ *              Added initialization for the pinned entry related fields.
+ *
+ *              JRM -- 5/31/06
+ *              Added initialization for the trace_file_ptr field.
+ *
+ *              JRM -- 8/19/06
+ *              Added initialization for the flush_in_progress field.
+ *
+ *              JRM -- 8/25/06
+ *              Added initialization for the slist_len_increase and
+ *              slist_size_increase fields.  These fields are used
+ *              for sanity checking in the flush process, and are not
+ *              compiled in unless H5C_DO_SANITY_CHECKS is TRUE.
+ *
+ *              JRM -- 3/28/07
+ *              Added initialization for the new is_read_only and
+ *              ro_ref_count fields.
+ *
+ *              JRM -- 7/27/07
+ *              Added initialization for the new evictions_enabled
+ *              field of H5C_t.
+ *
+ *              JRM -- 12/31/07
+ *              Added initialization for the new flash cache size increase
+ *              related fields of H5C_t.
+ *
+ *              JRM -- 11/5/08
+ *              Added initialization for the new clean_index_size and
+ *              dirty_index_size fields of H5C_t.
+ *
+ *
+ *              Missing entries?
+ *
+ *
+ *              JRM -- 4/20/20
+ *              Added initialization for the slist_enabled field.  Recall
+ *              that the slist is used to flush metadata cache entries 
+ *              in (roughly) increasing address order.  While this is 
+ *              needed at flush and close, it is not used elsewhere.
+ *              The slist_enabled field exists to allow us to construct 
+ *              the slist when needed, and leave it empty otherwise -- thus
+ *              avoiding the overhead of maintaining it.
+ *              
+ *                                               JRM -- 4/29/20
+ *              
  *-------------------------------------------------------------------------
  */
 H5C_t *
@@ -308,30 +384,36 @@ H5C_create(size_t		      max_cache_size,
     cache_ptr->dirty_index_size			= (size_t)0;
 
     for(i = 0; i < H5C_RING_NTYPES; i++) {
-	cache_ptr->index_ring_len[i]		= 0;
-	cache_ptr->index_ring_size[i]		= (size_t)0;
-	cache_ptr->clean_index_ring_size[i]	= (size_t)0;
-	cache_ptr->dirty_index_ring_size[i]	= (size_t)0;
+        cache_ptr->index_ring_len[i]            = 0;
+        cache_ptr->index_ring_size[i]           = (size_t)0;
+        cache_ptr->clean_index_ring_size[i]     = (size_t)0;
+        cache_ptr->dirty_index_ring_size[i]     = (size_t)0;
 
-	cache_ptr->slist_ring_len[i]		= 0;
-	cache_ptr->slist_ring_size[i]		= (size_t)0;
+        cache_ptr->slist_ring_len[i]            = 0;
+        cache_ptr->slist_ring_size[i]           = (size_t)0;
     } /* end for */
 
     for(i = 0; i < H5C__HASH_TABLE_LEN; i++)
         (cache_ptr->index)[i] = NULL;
 
-    cache_ptr->il_len				= 0;
-    cache_ptr->il_size				= (size_t)0;
-    cache_ptr->il_head				= NULL;
-    cache_ptr->il_tail				= NULL;
+    cache_ptr->il_len                           = 0;
+    cache_ptr->il_size                          = (size_t)0;
+    cache_ptr->il_head                          = NULL;
+    cache_ptr->il_tail                          = NULL;
 
     /* Tagging Field Initializations */
     cache_ptr->ignore_tags                      = FALSE;
     cache_ptr->num_objs_corked                  = 0;
 
-    cache_ptr->slist_changed			= FALSE;
-    cache_ptr->slist_len			= 0;
-    cache_ptr->slist_size			= (size_t)0;
+    /* slist field initializations */
+    cache_ptr->slist_enabled                    = ! H5C__SLIST_OPT_ENABLED;
+    cache_ptr->slist_changed                    = FALSE;
+    cache_ptr->slist_len                        = 0;
+    cache_ptr->slist_size                       = (size_t)0;
+
+    /* slist_ring_len, slist_ring_size, and 
+     * slist_ptr initializaed above.
+     */
 
 #if H5C_DO_SANITY_CHECKS
     cache_ptr->slist_len_increase		= 0;
@@ -825,6 +907,20 @@ done:
  * Programmer:  John Mainzer
  *		6/2/04
  *
+ * Modifications:
+ *
+ *              JRM -- 5/15/20
+ *
+ *              Updated the function to enable the slist prior to the 
+ *              call to H5C__flush_invalidate_cache().  
+ *
+ *              Arguably, it shouldn't be necessary to re-enable the
+ *              slist after the call to H5C__flush_invalidate_cache(), as 
+ *              the metadata cache should be discarded.  However, in the
+ *              test code, we make multiple calls to H5C_dest().  Thus 
+ *              we re-enable the slist on failure if it and the cache
+ *              still exist.
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
@@ -845,33 +941,60 @@ H5C_dest(H5F_t * f)
         HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't display cache image stats")
 #endif /* H5AC_DUMP_IMAGE_STATS_ON_CLOSE */
 
+    /* Enable the slist, as it is needed in the flush */
+    if ( H5C_set_slist_enabled(f->shared->cache, TRUE, FALSE) < 0 )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "set slist enabled failed")
+
     /* Flush and invalidate all cache entries */
-    if(H5C__flush_invalidate_cache(f, H5C__NO_FLAGS_SET) < 0 )
+    if ( H5C__flush_invalidate_cache(f, H5C__NO_FLAGS_SET) < 0 )
+
         HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "unable to flush cache")
 
     /* Generate & write cache image if requested */
-    if(cache_ptr->image_ctl.generate_image)
-        if(H5C__generate_cache_image(f, cache_ptr) < 0)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTCREATE, FAIL, "Can't generate metadata cache image")
+    if ( cache_ptr->image_ctl.generate_image ) {
+
+        if ( H5C__generate_cache_image(f, cache_ptr) < 0 )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTCREATE, FAIL, \
+                        "Can't generate metadata cache image")
+    }
+
+    /* Question: Is it possible for cache_ptr->slist be non-null at this 
+     *           point?  If no, shouldn't this if statement be an assert?
+     */
+    if ( cache_ptr->slist_ptr != NULL ) {
+
+        HDassert(cache_ptr->slist_len == 0);
+        HDassert(cache_ptr->slist_size == 0);
 
-    if(cache_ptr->slist_ptr != NULL) {
         H5SL_close(cache_ptr->slist_ptr);
+
         cache_ptr->slist_ptr = NULL;
+
     } /* end if */
 
     if(cache_ptr->tag_list != NULL) {
+
         H5SL_destroy(cache_ptr->tag_list, H5C_free_tag_list_cb, NULL);
         cache_ptr->tag_list = NULL;
+
     } /* end if */
 
-    if(cache_ptr->log_info != NULL)
+    if(cache_ptr->log_info != NULL) {
+
         H5MM_xfree(cache_ptr->log_info);
+    }
 
 #ifndef NDEBUG
 #if H5C_DO_SANITY_CHECKS
-    if(cache_ptr->get_entry_ptr_from_addr_counter > 0)
-        HDfprintf(stdout, "*** %ld calls to H5C_get_entry_ptr_from_add(). ***\n",
-                cache_ptr->get_entry_ptr_from_addr_counter);
+
+    if ( cache_ptr->get_entry_ptr_from_addr_counter > 0 ) {
+
+        HDfprintf(stdout, 
+                 "*** %ld calls to H5C_get_entry_ptr_from_add(). ***\n",
+                 cache_ptr->get_entry_ptr_from_addr_counter);
+    }
 #endif /* H5C_DO_SANITY_CHECKS */
 
     cache_ptr->magic = 0;
@@ -880,7 +1003,19 @@ H5C_dest(H5F_t * f)
     cache_ptr = H5FL_FREE(H5C_t, cache_ptr);
 
 done:
+
+    if ( ( ret_value < 0 ) && ( cache_ptr ) && ( cache_ptr->slist_ptr ) ) {
+
+        /* need this for test code -- see change note for details */
+
+        if ( H5C_set_slist_enabled(f->shared->cache, FALSE, FALSE) < 0 )
+
+            HDONE_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                        "disable slist on flush dest failure failed")
+    }
+
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5C_dest() */
 
 
@@ -894,6 +1029,14 @@ done:
  * Programmer:  Vailin Choi
  *		Dec 2013
  *
+ * Modifications:
+ *
+ *              JRM -- 5/5/20
+ *
+ *              Added code to enable the skip list prior to the call
+ *              to H5C__flush_invalidate_cache(), and disable it 
+ *              afterwards. 
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
@@ -906,9 +1049,22 @@ H5C_evict(H5F_t * f)
     /* Sanity check */
     HDassert(f);
 
+    /* Enable the slist, as it is needed in the flush */
+    if ( H5C_set_slist_enabled(f->shared->cache, TRUE, FALSE) < 0 )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "set slist enabled failed")
+
     /* Flush and invalidate all cache entries except the pinned entries */
-    if(H5C__flush_invalidate_cache(f, H5C__EVICT_ALLOW_LAST_PINS_FLAG) < 0 )
-        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "unable to evict entries in the cache")
+    if ( H5C__flush_invalidate_cache(f, H5C__EVICT_ALLOW_LAST_PINS_FLAG) < 0 )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, 
+                    "unable to evict entries in the cache")
+
+    /* Disable the slist,
+     */
+    if ( H5C_set_slist_enabled(f->shared->cache, FALSE, TRUE) < 0)
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "set slist disabled failed")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -2878,6 +3034,179 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ *
+ * Function:    H5C_set_slist_enabled()
+ *
+ * Purpose:     Enable or disable the slist as directed.
+ *
+ *              The slist (skip list) is an address ordered list of 
+ *              dirty entries in the metadata cache.  However, this 
+ *              list is only needed during flush and close, where we
+ *              use it to write entries in more or less increasing 
+ *              address order. 
+ *
+ *              This function sets up and enables further operations
+ *              on the slist, or disable the slist.  This in turn 
+ *              allows us to avoid the overhead of maintaining the 
+ *              slist when it is not needed.
+ *
+ *
+ *              If the slist_enabled parameter is TRUE, the function 
+ *              
+ *              1) Verifies that the slist is empty.
+ *
+ *              2) Scans the index list, and inserts all dirty entries
+ *                 into the slist.
+ *
+ *              3) Sets cache_ptr->slist_enabled = TRUE.
+ *
+ *              Note that the clear_slist parameter is ignored if 
+ *              the slist_enabed parameter is TRUE.
+ *
+ *
+ *              If the slist_enabled_parameter is FALSE, the function
+ *              shuts down the slist.
+ *
+ *              Normally the slist will be empty at this point, however
+ *              that need not be the case if H5C_flush_cache() has been
+ *              called with the H5C__FLUSH_MARKED_ENTRIES_FLAG.
+ *
+ *              Thus shutdown proceeds as follows:
+ *
+ *              1) Test to see if the slist is empty.  If it is, proceed
+ *                 to step 3. 
+ *
+ *              2) Test to see if the clear_slist parameter is TRUE.
+ *
+ *                 If it is, remove all entries from the slist.
+ *
+ *                 If it isn't, throw an error.
+ *
+ *              3) set cache_ptr->slist_enabled = FALSE.
+ *              
+ * Return:      SUCCEED on success, and FAIL on failure.
+ *
+ * Programmer:  John Mainzer
+ *              5/1/20
+ *
+ * Modifications:
+ *
+ *              None.
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5C_set_slist_enabled(H5C_t *cache_ptr, hbool_t slist_enabled, 
+    hbool_t clear_slist)
+{
+    H5C_cache_entry_t * entry_ptr;
+    herr_t ret_value = SUCCEED;      /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    if ( ( cache_ptr == NULL ) || ( cache_ptr->magic != H5C__H5C_T_MAGIC ) )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Bad cache_ptr on entry")
+
+#if H5C__SLIST_OPT_ENABLED
+
+    if ( slist_enabled ) {
+
+        if ( cache_ptr->slist_enabled ) {
+
+            HDassert(FALSE);
+            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "slist already enabled?")
+        }
+
+        if ( ( cache_ptr->slist_len != 0 ) ||
+             ( cache_ptr->slist_size != 0 ) ) {
+
+            HDassert(FALSE);
+            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "slist not empty (1)?")
+        }
+
+
+        /* set cache_ptr->slist_enabled to TRUE so that the slist 
+         * mainenance macros will be enabled.
+         */
+        cache_ptr->slist_enabled = TRUE;
+
+
+        /* scan the index list and insert all dirty entries in the slist */
+        entry_ptr = cache_ptr->il_head; 
+
+        while ( entry_ptr != NULL ) {
+
+            HDassert( entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC );
+
+            if ( entry_ptr->is_dirty ) {
+
+                H5C__INSERT_ENTRY_IN_SLIST(cache_ptr, entry_ptr, FAIL)
+            }
+
+            entry_ptr = entry_ptr->il_next;
+        }
+
+        /* we don't maintain a dirty index len, so we can't do a cross 
+         * check against it.  Note that there is no point in cross checking
+         * against the dirty LRU size, as the dirty LRU may not be maintained,
+         * and in any case, there is no requirement that all dirty entries 
+         * will reside on the dirty LRU.
+         */
+        HDassert( cache_ptr->dirty_index_size == cache_ptr->slist_size );
+
+    } else { /* take down the skip list */
+
+        if ( ! cache_ptr->slist_enabled ) {
+
+            HDassert(FALSE);
+            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "slist already disabled?")
+        }
+
+        if ( ( cache_ptr->slist_len != 0 ) ||
+             ( cache_ptr->slist_size != 0 ) ) {
+
+            if ( clear_slist ) {
+
+                H5SL_node_t *node_ptr;
+
+                node_ptr = H5SL_first(cache_ptr->slist_ptr);
+
+                while ( node_ptr != NULL ) {
+
+                    entry_ptr = (H5C_cache_entry_t *)H5SL_item(node_ptr);
+
+                    H5C__REMOVE_ENTRY_FROM_SLIST(cache_ptr, entry_ptr, FALSE);
+
+                    node_ptr = H5SL_first(cache_ptr->slist_ptr);
+                }
+            } else {
+ 
+                HDassert(FALSE);
+                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "slist not empty (2)?")
+            }
+        }
+
+        cache_ptr->slist_enabled = FALSE;
+
+        HDassert( 0 == cache_ptr->slist_len );
+        HDassert( 0 == cache_ptr->slist_size );
+    }
+
+#else /* H5C__SLIST_OPT_ENABLED is FALSE */
+
+    HDassert(cache_ptr->slist_enabled);
+
+#endif /* H5C__SLIST_OPT_ENABLED is FALSE */
+    
+done:
+
+    FUNC_LEAVE_NOAPI(ret_value)
+
+} /* H5C_set_slist_enabled() */
+
+
+/*-------------------------------------------------------------------------
  * Function:    H5C_unpin_entry()
  *
  * Purpose:	Unpin a cache entry.  The entry can be either protected or
@@ -2888,8 +3217,8 @@ done:
  * Programmer:  John Mainzer
  *              3/22/06
  *
- * Changes:	Added extreme sanity checks on entry and exit.
-                				JRM -- 4/26/14
+ * Changes:     Added extreme sanity checks on entry and exit.
+ *                                      JRM -- 4/26/14
  *
  *-------------------------------------------------------------------------
  */
@@ -2955,6 +3284,81 @@ done:
  * Programmer:  John Mainzer
  *              6/2/04
  *
+ * Modifications:
+ *
+ *              JRM -- 7/21/04
+ *              Updated for the addition of the hash table.
+ *
+ *              JRM -- 10/28/04
+ *              Added code to set cache_full to TRUE whenever we try to
+ *              make space in the cache.
+ *
+ *              JRM -- 11/12/04
+ *              Added code to call to H5C_make_space_in_cache() after the
+ *              call to H5C__auto_adjust_cache_size() if that function
+ *              sets the size_decreased flag is TRUE.
+ *
+ *              JRM -- 4/25/05
+ *              The size_decreased flag can also be set to TRUE in
+ *              H5C_set_cache_auto_resize_config() if a new configuration
+ *              forces an immediate reduction in cache size.  Modified
+ *              the code to deal with this eventuallity.
+ *
+ *              JRM -- 6/24/05
+ *              Added support for the new write_permitted field of H5C_t.
+ *
+ *              JRM -- 10/22/05
+ *              Hand optimizations.
+ *
+ *              JRM -- 5/3/06
+ *              Added code to set the new dirtied field in
+ *              H5C_cache_entry_t to FALSE prior to return.
+ *
+ *              JRM -- 6/23/06
+ *              Modified code to allow dirty entries to be loaded from
+ *              disk.  This is necessary as a bug fix in the object
+ *              header code requires us to modify a header as it is read.
+ *
+ *              JRM -- 3/28/07
+ *              Added the flags parameter and supporting code.  At least
+ *              for now, this parameter is used to allow the entry to
+ *              be protected read only, thus allowing multiple protects.
+ *
+ *              Also added code to allow multiple read only protects
+ *              of cache entries.
+ *
+ *              JRM -- 7/27/07
+ *              Added code supporting the new evictions_enabled field
+ *              in H5C_t.
+ *
+ *              JRM -- 1/3/08
+ *              Added to do a flash cache size increase if appropriate
+ *              when a large entry is loaded.
+ *
+ *              JRM -- 11/13/08
+ *              Modified function to call H5C_make_space_in_cache() when
+ *              the min_clean_size is violated, not just when there isn't
+ *              enough space for and entry that has just been loaded.
+ *
+ *              The purpose of this modification is to avoid "metadata
+ *              blizzards" in the write only case.  In such instances,
+ *              the cache was allowed to fill with dirty metadata.  When
+ *              we finally needed to evict an entry to make space, we had
+ *              to flush out a whole cache full of metadata -- which has
+ *              interesting performance effects.  We hope to avoid (or
+ *              perhaps more accurately hide) this effect by maintaining
+ *              the min_clean_size, which should force us to start flushing
+ *              entries long before we actually have to evict something
+ *              to make space.
+ *
+ *
+ *              Missing entries?
+ *
+ *
+ *              JRM -- 5/8/20
+ *              Updated for the possibility that the slist will be 
+ *              disabled.
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
@@ -2996,9 +3400,15 @@ H5C_unprotect(H5F_t *f, haddr_t	addr, void *thing, unsigned flags)
     HDassert( H5F_addr_defined(addr) );
     HDassert( thing );
     HDassert( ! ( pin_entry && unpin_entry ) );
-    HDassert( ( ! free_file_space ) || ( deleted ) );   /* deleted flag must accompany free_file_space */
-    HDassert( ( ! take_ownership ) || ( deleted ) );    /* deleted flag must accompany take_ownership */
-    HDassert( ! ( free_file_space && take_ownership ) );    /* can't have both free_file_space & take_ownership */
+
+    /* deleted flag must accompany free_file_space */
+    HDassert( ( ! free_file_space ) || ( deleted ) );
+
+    /* deleted flag must accompany take_ownership */
+    HDassert( ( ! take_ownership ) || ( deleted ) );
+
+    /* can't have both free_file_space & take_ownership */
+    HDassert( ! ( free_file_space && take_ownership ) );
 
     entry_ptr = (H5C_cache_entry_t *)thing;
 
@@ -3011,48 +3421,66 @@ H5C_unprotect(H5F_t *f, haddr_t	addr, void *thing, unsigned flags)
     was_clean = ! ( entry_ptr->is_dirty );
 
 #if H5C_DO_EXTREME_SANITY_CHECKS
-    if((H5C_validate_protected_entry_list(cache_ptr) < 0) ||
-            (H5C_validate_pinned_entry_list(cache_ptr) < 0) ||
-            (H5C_validate_lru_list(cache_ptr) < 0))
-        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "an extreme sanity check failed on entry")
+    if ( ( H5C_validate_protected_entry_list(cache_ptr) < 0 ) ||
+         ( H5C_validate_pinned_entry_list(cache_ptr) < 0 ) ||
+         ( H5C_validate_lru_list(cache_ptr) < 0 ) )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                    "an extreme sanity check failed on entry")
 #endif /* H5C_DO_EXTREME_SANITY_CHECKS */
 
     /* if the entry has multiple read only protects, just decrement
      * the ro_ref_counter.  Don't actually unprotect until the ref count
      * drops to zero.
      */
-    if(entry_ptr->ro_ref_count > 1) {
+    if ( entry_ptr->ro_ref_count > 1 ) {
+
         /* Sanity check */
-	HDassert(entry_ptr->is_protected);
+        HDassert(entry_ptr->is_protected);
         HDassert(entry_ptr->is_read_only);
 
-	if(dirtied)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, "Read only entry modified??")
+        if ( dirtied )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, \
+                        "Read only entry modified??")
 
         /* Reduce the RO ref count */
-	(entry_ptr->ro_ref_count)--;
+        (entry_ptr->ro_ref_count)--;
 
         /* Pin or unpin the entry as requested. */
-        if(pin_entry) {
+        if ( pin_entry ) {
+
             /* Pin the entry from a client */
-            if(H5C__pin_entry_from_client(cache_ptr, entry_ptr) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTPIN, FAIL, "Can't pin entry by client")
-        } else if(unpin_entry) {
+            if ( H5C__pin_entry_from_client(cache_ptr, entry_ptr) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTPIN, FAIL, \
+                            "Can't pin entry by client")
+
+        } else if ( unpin_entry ) {
+
             /* Unpin the entry from a client */
-            if(H5C__unpin_entry_from_client(cache_ptr, entry_ptr, FALSE) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPIN, FAIL, "Can't unpin entry by client")
+            if ( H5C__unpin_entry_from_client(cache_ptr, entry_ptr, FALSE) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPIN, FAIL, \
+                            "Can't unpin entry by client")
+
         } /* end if */
     } else {
-	if(entry_ptr->is_read_only) {
+
+        if ( entry_ptr->is_read_only ) {
+
             /* Sanity check */
-	    HDassert(entry_ptr->ro_ref_count == 1);
+            HDassert(entry_ptr->ro_ref_count == 1);
 
-	    if(dirtied)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, "Read only entry modified??")
+            if ( dirtied )
 
-	    entry_ptr->is_read_only = FALSE;
-	    entry_ptr->ro_ref_count = 0;
-	} /* end if */
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, \
+                            "Read only entry modified??")
+
+            entry_ptr->is_read_only = FALSE;
+            entry_ptr->ro_ref_count = 0;
+
+        } /* end if */
 
 #ifdef H5_HAVE_PARALLEL
         /* When the H5C code is used to implement the metadata cache in the
@@ -3080,63 +3508,102 @@ H5C_unprotect(H5F_t *f, haddr_t	addr, void *thing, unsigned flags)
         } /* end if */
 #endif /* H5_HAVE_PARALLEL */
 
-        if(!entry_ptr->is_protected)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, "Entry already unprotected??")
+        if ( ! entry_ptr->is_protected )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, \
+                        "Entry already unprotected??")
 
         /* Mark the entry as dirty if appropriate */
         entry_ptr->is_dirty = (entry_ptr->is_dirty || dirtied);
 
-	if(dirtied)
-	    if(entry_ptr->image_up_to_date) {
-	        entry_ptr->image_up_to_date = FALSE;
-	        if(entry_ptr->flush_dep_nparents > 0)
-		    if(H5C__mark_flush_dep_unserialized(entry_ptr) < 0)
-                        HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, "Can't propagate serialization status to fd parents")
+        if ( dirtied ) {
+
+            if ( entry_ptr->image_up_to_date ) {
+
+                entry_ptr->image_up_to_date = FALSE;
+
+                if ( entry_ptr->flush_dep_nparents > 0 ) {
+
+                    if ( H5C__mark_flush_dep_unserialized(entry_ptr) < 0 )
+
+                        HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, \
+                          "Can't propagate serialization status to fd parents")
+
+                } /* end if */
             } /* end if */
+        } /* end if */
 
         /* Check for newly dirtied entry */
-        if(was_clean && entry_ptr->is_dirty) {
+        if ( was_clean && entry_ptr->is_dirty ) {
+
             /* Update index for newly dirtied entry */
             H5C__UPDATE_INDEX_FOR_ENTRY_DIRTY(cache_ptr, entry_ptr)
 
-            /* If the entry's type has a 'notify' callback send a 'entry dirtied'
-             * notice now that the entry is fully integrated into the cache.
+            /* If the entry's type has a 'notify' callback send a 
+             * 'entry dirtied' notice now that the entry is fully 
+             * integrated into the cache.
              */
-            if(entry_ptr->type->notify &&
-                    (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_ENTRY_DIRTIED, entry_ptr) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, "can't notify client about entry dirty flag set")
+            if ( ( entry_ptr->type->notify ) &&
+                 ( (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_ENTRY_DIRTIED, 
+                                             entry_ptr) < 0 ) )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, \
+                            "can't notify client about entry dirty flag set")
 
             /* Propagate the flush dep dirty flag up the flush dependency chain
-             * if appropriate */
-            if(entry_ptr->flush_dep_nparents > 0)
-                if(H5C__mark_flush_dep_dirty(entry_ptr) < 0)
-                    HGOTO_ERROR(H5E_CACHE, H5E_CANTMARKDIRTY, FAIL, "Can't propagate flush dep dirty flag")
+             * if appropriate 
+             */
+            if ( entry_ptr->flush_dep_nparents > 0 ) {
+
+                if ( H5C__mark_flush_dep_dirty(entry_ptr) < 0 )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_CANTMARKDIRTY, FAIL, \
+                                "Can't propagate flush dep dirty flag")
+            }
         } /* end if */
         /* Check for newly clean entry */
-        else if(!was_clean && !entry_ptr->is_dirty) {
-            /* If the entry's type has a 'notify' callback send a 'entry cleaned'
-             * notice now that the entry is fully integrated into the cache.
+        else if ( ! was_clean && ! entry_ptr->is_dirty ) {
+
+            /* If the entry's type has a 'notify' callback send a 
+             * 'entry cleaned' notice now that the entry is fully 
+             * integrated into the cache.
              */
-            if(entry_ptr->type->notify &&
-                    (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_ENTRY_CLEANED, entry_ptr) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, "can't notify client about entry dirty flag cleared")
+            if ( ( entry_ptr->type->notify ) &&
+                 ( (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_ENTRY_CLEANED, 
+                                             entry_ptr) < 0 ) )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, \
+                          "can't notify client about entry dirty flag cleared")
 
             /* Propagate the flush dep clean flag up the flush dependency chain
-             * if appropriate */
-            if(entry_ptr->flush_dep_nparents > 0)
-                if(H5C__mark_flush_dep_clean(entry_ptr) < 0)
-                    HGOTO_ERROR(H5E_CACHE, H5E_CANTMARKDIRTY, FAIL, "Can't propagate flush dep dirty flag")
+             * if appropriate 
+             */
+            if ( entry_ptr->flush_dep_nparents > 0 ) {
+
+                if ( H5C__mark_flush_dep_clean(entry_ptr) < 0 )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_CANTMARKDIRTY, FAIL, \
+                                "Can't propagate flush dep dirty flag")
+        
+            }   
         } /* end else-if */
 
         /* Pin or unpin the entry as requested. */
-        if(pin_entry) {
+        if ( pin_entry ) {
+
             /* Pin the entry from a client */
-            if(H5C__pin_entry_from_client(cache_ptr, entry_ptr) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTPIN, FAIL, "Can't pin entry by client")
-        } else if(unpin_entry) {
+            if ( H5C__pin_entry_from_client(cache_ptr, entry_ptr) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTPIN, FAIL, \
+                            "Can't pin entry by client")
+
+        } else if ( unpin_entry ) {
+
             /* Unpin the entry from a client */
-            if(H5C__unpin_entry_from_client(cache_ptr, entry_ptr, FALSE) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPIN, FAIL, "Can't unpin entry by client")
+            if ( H5C__unpin_entry_from_client(cache_ptr, entry_ptr, FALSE) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPIN, FAIL, \
+                            "Can't unpin entry by client")
         } /* end if */
 
         /* H5C__UPDATE_RP_FOR_UNPROTECT will place the unprotected entry on
@@ -3149,10 +3616,15 @@ H5C_unprotect(H5F_t *f, haddr_t	addr, void *thing, unsigned flags)
         /* if the entry is dirty, 'or' its flush_marker with the set flush flag,
          * and then add it to the skip list if it isn't there already.
          */
-        if(entry_ptr->is_dirty) {
+        if ( entry_ptr->is_dirty ) {
+
             entry_ptr->flush_marker |= set_flush_marker;
-            if(!entry_ptr->in_slist)
+
+            if ( !entry_ptr->in_slist ) {
+
+                /* this is a no-op if cache_ptr->slist_enabled is FALSE */ 
                 H5C__INSERT_ENTRY_IN_SLIST(cache_ptr, entry_ptr, FAIL)
+            }
         } /* end if */
 
         /* this implementation of the "deleted" option is a bit inefficient, as
@@ -3164,44 +3636,71 @@ H5C_unprotect(H5F_t *f, haddr_t	addr, void *thing, unsigned flags)
          * makes good use of existing code.
          *                                             JRM - 5/19/04
          */
-        if(deleted) {
-            unsigned    flush_flags = (H5C__FLUSH_CLEAR_ONLY_FLAG |
-                                         H5C__FLUSH_INVALIDATE_FLAG);
+        if ( deleted ) {
+
+            unsigned flush_flags = (H5C__FLUSH_CLEAR_ONLY_FLAG |
+                                    H5C__FLUSH_INVALIDATE_FLAG);
 
             /* verify that the target entry is in the cache. */
             H5C__SEARCH_INDEX(cache_ptr, addr, test_entry_ptr, FAIL)
-            if(test_entry_ptr == NULL)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, "entry not in hash table?!?")
-            else if(test_entry_ptr != entry_ptr)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, "hash table contains multiple entries for addr?!?")
+
+            if ( test_entry_ptr == NULL )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, \
+                                "entry not in hash table?!?")
+
+            else if ( test_entry_ptr != entry_ptr )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, \
+                        "hash table contains multiple entries for addr?!?")
 
             /* Set the 'free file space' flag for the flush, if needed */
-            if(free_file_space)
+            if ( free_file_space ) {
+
                 flush_flags |= H5C__FREE_FILE_SPACE_FLAG;
+            }
 
             /* Set the "take ownership" flag for the flush, if needed */
-            if(take_ownership)
+            if ( take_ownership ) {
+
                 flush_flags |= H5C__TAKE_OWNERSHIP_FLAG;
+            }
 
             /* Delete the entry from the skip list on destroy */
             flush_flags |= H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG;
 
-            HDassert(((!was_clean) || dirtied) == entry_ptr->in_slist);
-            if(H5C__flush_single_entry(f, entry_ptr, flush_flags) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, "Can't flush entry")
+            HDassert( ( ! cache_ptr->slist_enabled ) || \
+                      ( ( ( ! was_clean ) || dirtied ) == \
+                        ( entry_ptr->in_slist ) ) );
+
+            if ( H5C__flush_single_entry(f, entry_ptr, flush_flags) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, \
+                            "Can't flush entry")
+
         } /* end if */
 #ifdef H5_HAVE_PARALLEL
-        else if(clear_entry) {
+        else if ( clear_entry ) {
 
             /* verify that the target entry is in the cache. */
             H5C__SEARCH_INDEX(cache_ptr, addr, test_entry_ptr, FAIL)
-            if(test_entry_ptr == NULL)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, "entry not in hash table?!?")
-            else if(test_entry_ptr != entry_ptr)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, "hash table contains multiple entries for addr?!?")
 
-            if(H5C__flush_single_entry(f, entry_ptr, H5C__FLUSH_CLEAR_ONLY_FLAG | H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, "Can't clear entry")
+            if ( test_entry_ptr == NULL ) 
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, \
+                            "entry not in hash table?!?")
+
+            else if ( test_entry_ptr != entry_ptr )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, \
+                            "hash table contains multiple entries for addr?!?")
+
+            if ( H5C__flush_single_entry(f, entry_ptr, 
+                                      H5C__FLUSH_CLEAR_ONLY_FLAG | 
+                                      H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG) < 0 )
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTUNPROTECT, FAIL, \
+                            "Can't clear entry")
+
         } /* end else if */
 #endif /* H5_HAVE_PARALLEL */
     }
@@ -3209,14 +3708,18 @@ H5C_unprotect(H5F_t *f, haddr_t	addr, void *thing, unsigned flags)
     H5C__UPDATE_STATS_FOR_UNPROTECT(cache_ptr)
 
 done:
+
 #if H5C_DO_EXTREME_SANITY_CHECKS
-    if((H5C_validate_protected_entry_list(cache_ptr) < 0) ||
-            (H5C_validate_pinned_entry_list(cache_ptr) < 0) ||
-            (H5C_validate_lru_list(cache_ptr) < 0)) {
-        HDONE_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "an extreme sanity check failed on exit")
+    if ( ( H5C_validate_protected_entry_list(cache_ptr) < 0 ) ||
+         ( H5C_validate_pinned_entry_list(cache_ptr) < 0 ) ||
+         ( H5C_validate_lru_list(cache_ptr) < 0 ) ) {
+
+        HDONE_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                    "an extreme sanity check failed on exit")
 #endif /* H5C_DO_EXTREME_SANITY_CHECKS */
 
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5C_unprotect() */
 
 
@@ -5028,6 +5531,7 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ *
  * Function:    H5C__flush_invalidate_cache
  *
  * Purpose:	Flush and destroy the entries contained in the target
@@ -5057,6 +5561,51 @@ done:
  * Programmer:  John Mainzer
  *		3/24/065
  *
+ * Modifications:
+ *
+ *              To support the fractal heap, the cache must now deal with
+ *              entries being dirtied, resized, and/or renamed inside
+ *              flush callbacks.  Updated function to support this.
+ *
+ *                                                   -- JRM 8/27/06
+ *
+ *              Added code to detect and manage the case in which a
+ *              flush callback changes the s-list out from under
+ *              the function.  The only way I can think of in which this
+ *              can happen is if a flush function loads an entry
+ *              into the cache that isn't there already.  Quincey tells
+ *              me that this will never happen, but I'm not sure I
+ *              believe him.
+ *
+ *              Note that this is a pretty bad scenario if it ever
+ *              happens.  The code I have added should allow us to
+ *              handle the situation under all but the worst conditions,
+ *              but one can argue that we should just scream and die if 
+ *              we ever detect the condition.
+ *
+ *                                                      -- JRM 10/13/07
+ *
+ *              Missing entries?
+ *
+ *
+ *              Added support for the H5C__EVICT_ALLOW_LAST_PINS_FLAG.
+ *              This flag is used to flush and evict all entries in 
+ *              the metadata cache that are not pinned -- typically,
+ *              everything other than the superblock.
+ *
+ *                                           ??? -- ??/??/??
+ *
+ *              Added sanity checks to verify that the skip list is 
+ *              enabled on entry.  On the face of it, it would make 
+ *              sense to enable the slist on entry, and disable it 
+ *              on exit, as this function is not called repeatedly.
+ *              However, since this function can be called from
+ *              H5C_flush_cache(), this would create cases in the test
+ *              code where we would have to check the flags to determine
+ *              whether we must setup and take down the slist.
+ *
+ *                                           JRM -- 5/5/20
+ *
  *-------------------------------------------------------------------------
  */
 static herr_t
@@ -5074,6 +5623,7 @@ H5C__flush_invalidate_cache(H5F_t *f, unsigned flags)
     HDassert(cache_ptr);
     HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);
     HDassert(cache_ptr->slist_ptr);
+    HDassert(cache_ptr->slist_enabled);
 
 #if H5C_DO_SANITY_CHECKS
 {
@@ -5092,7 +5642,8 @@ H5C__flush_invalidate_cache(H5F_t *f, unsigned flags)
     HDassert(cache_ptr->slist_ring_len[H5C_RING_UNDEFINED] == 0);
     HDassert(cache_ptr->slist_ring_size[H5C_RING_UNDEFINED] == (size_t)0);
 
-    for(i = H5C_RING_USER; i < H5C_RING_NTYPES; i++) {
+    for ( i = H5C_RING_USER; i < H5C_RING_NTYPES; i++ ) {
+
         index_len += cache_ptr->index_ring_len[i];
         index_size += cache_ptr->index_ring_size[i];
         clean_index_size += cache_ptr->clean_index_ring_size[i];
@@ -5100,6 +5651,7 @@ H5C__flush_invalidate_cache(H5F_t *f, unsigned flags)
 
         slist_len += cache_ptr->slist_ring_len[i];
         slist_size += cache_ptr->slist_ring_size[i];
+
     } /* end for */
 
     HDassert(cache_ptr->index_len == index_len);
@@ -5112,49 +5664,68 @@ H5C__flush_invalidate_cache(H5F_t *f, unsigned flags)
 #endif /* H5C_DO_SANITY_CHECKS */
 
     /* remove ageout markers if present */
-    if(cache_ptr->epoch_markers_active > 0)
-        if(H5C__autoadjust__ageout__remove_all_markers(cache_ptr) < 0)
-            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "error removing all epoch markers")
+    if ( cache_ptr->epoch_markers_active > 0 ) {
+
+        if ( H5C__autoadjust__ageout__remove_all_markers(cache_ptr) < 0 )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                        "error removing all epoch markers")
+    }
 
     /* flush invalidate each ring, starting from the outermost ring and
      * working inward.
      */
     ring = H5C_RING_USER;
-    while(ring < H5C_RING_NTYPES) {
+
+    while ( ring < H5C_RING_NTYPES)  {
+
         if(H5C_flush_invalidate_ring(f, ring, flags) < 0)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "flush invalidate ring failed")
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, 
+                        "flush invalidate ring failed")
         ring++;
+
     } /* end while */
 
     /* Invariants, after destroying all entries in the hash table */
-    if(!(flags & H5C__EVICT_ALLOW_LAST_PINS_FLAG)) {
+    if( ! ( flags & H5C__EVICT_ALLOW_LAST_PINS_FLAG ) ) {
+
         HDassert(cache_ptr->index_size == 0);
         HDassert(cache_ptr->clean_index_size == 0);
         HDassert(cache_ptr->pel_len == 0);
         HDassert(cache_ptr->pel_size == 0);
+
     } /* end if */
     else {
+
         H5C_cache_entry_t *entry_ptr;   /* Cache entry */
         unsigned u;                     /* Local index variable */
 
         /* All rings except ring 4 should be empty now */
         /* (Ring 4 has the superblock) */
-        for(u = H5C_RING_USER; u < H5C_RING_SB; u++) {
+        for ( u = H5C_RING_USER; u < H5C_RING_SB; u++ ) {
+
             HDassert(cache_ptr->index_ring_len[u] == 0);
             HDassert(cache_ptr->index_ring_size[u] == 0);
             HDassert(cache_ptr->clean_index_ring_size[u] == 0);
+
         } /* end for */
 
         /* Check that any remaining pinned entries are in the superblock ring */
+
         entry_ptr = cache_ptr->pel_head_ptr;
+
         while(entry_ptr) {
+
             /* Check ring */
             HDassert(entry_ptr->ring == H5C_RING_SB);
 
             /* Advance to next entry in pinned entry list */
             entry_ptr = entry_ptr->next;
+
         } /* end while */
     } /* end else */
+
     HDassert(cache_ptr->dirty_index_size == 0);
     HDassert(cache_ptr->slist_len == 0);
     HDassert(cache_ptr->slist_size == 0);
@@ -5164,43 +5735,59 @@ H5C__flush_invalidate_cache(H5F_t *f, unsigned flags)
     HDassert(cache_ptr->LRU_list_size == 0);
 
 done:
+
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5C__flush_invalidate_cache() */
 
 
 /*-------------------------------------------------------------------------
  * Function:    H5C_flush_invalidate_ring
  *
- * Purpose:	Flush and destroy the entries contained in the target
- *		cache and ring.
+ * Purpose:     Flush and destroy the entries contained in the target
+ *              cache and ring.
  *
- *		If the ring contains protected entries, the function will
- *		fail, as protected entries cannot be either flushed or
- *		destroyed.  However all unprotected entries should be
- *		flushed and destroyed before the function returns failure.
+ *              If the ring contains protected entries, the function will
+ *              fail, as protected entries cannot be either flushed or
+ *              destroyed.  However all unprotected entries should be
+ *              flushed and destroyed before the function returns failure.
  *
- *		While pinned entries can usually be flushed, they cannot
- *		be destroyed.  However, they should be unpinned when all
- *		the entries that reference them have been destroyed (thus
- *		reduding the pinned entry's reference count to 0, allowing
- *		it to be unpinned).
+ *              While pinned entries can usually be flushed, they cannot
+ *              be destroyed.  However, they should be unpinned when all
+ *              the entries that reference them have been destroyed (thus
+ *              reduding the pinned entry's reference count to 0, allowing
+ *              it to be unpinned).
  *
- *		If pinned entries are present, the function makes repeated
- *		passes through the cache, flushing all dirty entries
- *		(including the pinned dirty entries where permitted) and
- *		destroying all unpinned entries.  This process is repeated
- *		until either the cache is empty, or the number of pinned
- *		entries stops decreasing on each pass.
+ *              If pinned entries are present, the function makes repeated
+ *              passes through the cache, flushing all dirty entries
+ *              (including the pinned dirty entries where permitted) and
+ *              destroying all unpinned entries.  This process is repeated
+ *              until either the cache is empty, or the number of pinned
+ *              entries stops decreasing on each pass.
  *
- *		If flush dependencies appear in the target ring, the
- *		function makes repeated passes through the cache flushing
- *		entries in flush dependency order.
+ *              If flush dependencies appear in the target ring, the
+ *              function makes repeated passes through the cache flushing
+ *              entries in flush dependency order.
  *
  * Return:      Non-negative on success/Negative on failure or if there was
- *		a request to flush all items and something was protected.
+ *              a request to flush all items and something was protected.
  *
  * Programmer:  John Mainzer
- *		9/1/15
+ *              9/1/15
+ *
+ * Changes:     Added support for the H5C__EVICT_ALLOW_LAST_PINS_FLAG.
+ *              This flag is used to flush and evict all entries in 
+ *              the metadata cache that are not pinned -- typically,
+ *              everything other than the superblock.
+ *
+ *                                           ??? -- ??/??/??
+ *
+ *              A recent optimization turns off the slist unless a flush
+ *              is in progress.  This should not effect this function, as
+ *              it is only called during a flush.  Added an assertion to 
+ *              verify this.
+ *
+ *                                           JRM -- 5/6/20
  *
  *-------------------------------------------------------------------------
  */
@@ -5228,9 +5815,12 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
 
     HDassert(f);
     HDassert(f->shared);
+
     cache_ptr = f->shared->cache;
+
     HDassert(cache_ptr);
     HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);
+    HDassert(cache_ptr->slist_enabled);
     HDassert(cache_ptr->slist_ptr);
     HDassert(ring > H5C_RING_UNDEFINED);
     HDassert(ring < H5C_RING_NTYPES);
@@ -5272,19 +5862,25 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
      */
 
     /* compute the number of pinned entries in this ring */
+
     entry_ptr = cache_ptr->pel_head_ptr;
     cur_ring_pel_len = 0;
-    while(entry_ptr != NULL) {
+
+    while ( entry_ptr != NULL ) {
+
         HDassert(entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC);
         HDassert(entry_ptr->ring >= ring);
         if(entry_ptr->ring == ring)
             cur_ring_pel_len++;
 
         entry_ptr = entry_ptr->next;
+
     } /* end while */
 
     old_ring_pel_len = cur_ring_pel_len;
+
     while(cache_ptr->index_ring_len[ring] > 0) {
+
         /* first, try to flush-destroy any dirty entries.   Do this by
          * making a scan through the slist.  Note that new dirty entries
          * may be created by the flush call backs.  Thus it is possible
@@ -5327,25 +5923,33 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
 
         /* this done, start the scan of the slist */
         restart_slist_scan = TRUE;
-        while(restart_slist_scan || (node_ptr != NULL)) {
-            if(restart_slist_scan) {
+
+        while ( restart_slist_scan || ( node_ptr != NULL ) ) {
+
+            if ( restart_slist_scan ) {
+
                 restart_slist_scan = FALSE;
 
                 /* Start at beginning of skip list */
                 node_ptr = H5SL_first(cache_ptr->slist_ptr);
-                if(node_ptr == NULL)
+
+                if ( node_ptr == NULL )
                     /* the slist is empty -- break out of inner loop */
                     break;
 
                 /* Get cache entry for this node */
                 next_entry_ptr = (H5C_cache_entry_t *)H5SL_item(node_ptr);
-                if(NULL == next_entry_ptr)
-                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "next_entry_ptr == NULL ?!?!")
+
+                if ( NULL == next_entry_ptr )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                                "next_entry_ptr == NULL ?!?!")
 
                 HDassert(next_entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC);
                 HDassert(next_entry_ptr->is_dirty);
                 HDassert(next_entry_ptr->in_slist);
                 HDassert(next_entry_ptr->ring >= ring);
+
             } /* end if */
 
             entry_ptr = next_entry_ptr;
@@ -5371,18 +5975,26 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
              * from the slist.
              */
             node_ptr = H5SL_next(node_ptr);
+
             if(node_ptr != NULL) {
+
                 next_entry_ptr = (H5C_cache_entry_t *)H5SL_item(node_ptr);
+
                 if(NULL == next_entry_ptr)
-                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "next_entry_ptr == NULL ?!?!")
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                                "next_entry_ptr == NULL ?!?!")
+
                 HDassert(next_entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC);
                 HDassert(next_entry_ptr->is_dirty);
                 HDassert(next_entry_ptr->in_slist);
                 HDassert(next_entry_ptr->ring >= ring);
                 HDassert(entry_ptr != next_entry_ptr);
             } /* end if */
-            else
+            else {
+
                 next_entry_ptr = NULL;
+            }
 
             /* Note that we now remove nodes from the slist as we flush
              * the associated entries, instead of leaving them there
@@ -5394,22 +6006,31 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
              * flush, we must keep the slist in canonical form at all
              * times.
              */
-            if(((!entry_ptr->flush_me_last) ||
-                    ((entry_ptr->flush_me_last) &&
-                        (cache_ptr->num_last_entries >= cache_ptr->slist_len))) &&
-                    (entry_ptr->flush_dep_nchildren == 0) &&
-                    (entry_ptr->ring == ring)) {
-                if(entry_ptr->is_protected) {
+            if ( ( ( !entry_ptr->flush_me_last ) ||
+                   ( ( entry_ptr->flush_me_last ) &&
+                     ( cache_ptr->num_last_entries >= cache_ptr->slist_len ) ) 
+                 ) &&
+                 ( entry_ptr->flush_dep_nchildren == 0 ) &&
+                 ( entry_ptr->ring == ring ) ) {
+
+                if ( entry_ptr->is_protected ) {
+
                     /* we have major problems -- but lets flush
                      * everything we can before we flag an error.
                      */
                     protected_entries++;
+
                 } /* end if */
-                else if(entry_ptr->is_pinned) {
-                    if(H5C__flush_single_entry(f, entry_ptr, H5C__DURING_FLUSH_FLAG) < 0)
-                        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "dirty pinned entry flush failed")
+                else if ( entry_ptr->is_pinned ) {
+
+                    if ( H5C__flush_single_entry(f, entry_ptr, 
+                                                 H5C__DURING_FLUSH_FLAG) < 0 )
+
+                        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                                    "dirty pinned entry flush failed")
+
+                    if ( cache_ptr->slist_changed ) {
 
-                    if(cache_ptr->slist_changed) {
                         /* The slist has been modified by something
                          * other than the simple removal of the
                          * of the flushed entry after the flush.
@@ -5420,13 +6041,22 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
                         restart_slist_scan = TRUE;
                         cache_ptr->slist_changed = FALSE;
                         H5C__UPDATE_STATS_FOR_SLIST_SCAN_RESTART(cache_ptr);
+
                     } /* end if */
                 } /* end else-if */
                 else {
-                    if(H5C__flush_single_entry(f, entry_ptr, (cooked_flags | H5C__DURING_FLUSH_FLAG | H5C__FLUSH_INVALIDATE_FLAG | H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG)) < 0)
-                        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "dirty entry flush destroy failed")
 
-                    if(cache_ptr->slist_changed) {
+                    if ( H5C__flush_single_entry(f, entry_ptr, 
+                                    (cooked_flags | 
+                                     H5C__DURING_FLUSH_FLAG | 
+                                     H5C__FLUSH_INVALIDATE_FLAG |
+                                     H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG) ) < 0)
+
+                        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, 
+                                    "dirty entry flush destroy failed")
+
+                    if ( cache_ptr->slist_changed ) {
+
                         /* The slist has been modified by something
                          * other than the simple removal of the
                          * of the flushed entry after the flush.
@@ -5452,9 +6082,15 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
          * out from under us.
          */
 
-        if(node_ptr == NULL) {
-            HDassert(cache_ptr->slist_len == (uint32_t)((int32_t)initial_slist_len + cache_ptr->slist_len_increase));
-            HDassert(cache_ptr->slist_size == (size_t)((ssize_t)initial_slist_size + cache_ptr->slist_size_increase));
+        if ( node_ptr == NULL ) {
+
+            HDassert(cache_ptr->slist_len == 
+                     (uint32_t)((int32_t)initial_slist_len + 
+                                 cache_ptr->slist_len_increase));
+
+            HDassert(cache_ptr->slist_size == 
+                     (size_t)((ssize_t)initial_slist_size + 
+                              cache_ptr->slist_size_increase));
         } /* end if */
 #endif /* H5C_DO_SANITY_CHECKS */
 
@@ -5478,7 +6114,9 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
         cache_ptr->entries_relocated_counter      = 0;
 
         next_entry_ptr = cache_ptr->il_head;
-        while(next_entry_ptr != NULL) {
+
+        while ( next_entry_ptr != NULL ) {
+
             entry_ptr = next_entry_ptr;
             HDassert(entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC);
             HDassert(entry_ptr->ring >= ring);
@@ -5487,18 +6125,28 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
             HDassert((next_entry_ptr == NULL) ||
                      (next_entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC));
 
-            if((!entry_ptr->flush_me_last || (entry_ptr->flush_me_last && cache_ptr->num_last_entries >= cache_ptr->slist_len))
-                    && entry_ptr->flush_dep_nchildren == 0 && entry_ptr->ring == ring) {
-                if(entry_ptr->is_protected) {
+            if ( ( ( ! entry_ptr->flush_me_last ) || 
+                   ( entry_ptr->flush_me_last && 
+                     ( cache_ptr->num_last_entries >= cache_ptr->slist_len ) ) 
+                 ) && 
+                 ( entry_ptr->flush_dep_nchildren == 0 ) && 
+                 ( entry_ptr->ring == ring ) ) {
+
+                if ( entry_ptr->is_protected ) {
+
                     /* we have major problems -- but lets flush and
                      * destroy everything we can before we flag an
                      * error.
                      */
                     protected_entries++;
-                    if(!entry_ptr->in_slist)
+
+                    if ( ! entry_ptr->in_slist ) {
+
                         HDassert(!(entry_ptr->is_dirty));
+                    }
                 } /* end if */
-                else if(!(entry_ptr->is_pinned)) {
+                else if ( ! ( entry_ptr->is_pinned ) ) {
+
                     /* if *entry_ptr is dirty, it is possible
                      * that one or more other entries may be
                      * either removed from the cache, loaded
@@ -5527,8 +6175,14 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
                      */
                     cache_ptr->entry_watched_for_removal = next_entry_ptr;
 
-                    if(H5C__flush_single_entry(f, entry_ptr, (cooked_flags | H5C__DURING_FLUSH_FLAG | H5C__FLUSH_INVALIDATE_FLAG | H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG)) < 0)
-                        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Entry flush destroy failed")
+                    if ( H5C__flush_single_entry(f, entry_ptr, 
+                                    (cooked_flags | 
+                                     H5C__DURING_FLUSH_FLAG | 
+                                     H5C__FLUSH_INVALIDATE_FLAG | 
+                                     H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG)) < 0 )
+
+                        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                                    "Entry flush destroy failed")
 
                     /* Restart the index list scan if necessary.  Must
                      * do this if the next entry is evicted, and also if
@@ -5538,10 +6192,12 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
                      * if this results in the size of the pinned entry
                      * failing to decline during the pass.
                      */
-                    if((NULL != next_entry_ptr && NULL == cache_ptr->entry_watched_for_removal)
-                            || (cache_ptr->entries_loaded_counter > 0)
-                            || (cache_ptr->entries_inserted_counter > 0)
-                            || (cache_ptr->entries_relocated_counter > 0)) {
+                    if ( ( ( NULL != next_entry_ptr ) && 
+                           ( NULL == cache_ptr->entry_watched_for_removal ) 
+                         ) ||
+                         ( cache_ptr->entries_loaded_counter > 0 ) ||
+                         ( cache_ptr->entries_inserted_counter > 0 ) ||
+                         ( cache_ptr->entries_relocated_counter > 0 ) ) {
 
                         next_entry_ptr = cache_ptr->il_head;
 
@@ -5550,9 +6206,12 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
                         cache_ptr->entries_relocated_counter      = 0;
 
                         H5C__UPDATE_STATS_FOR_INDEX_SCAN_RESTART(cache_ptr)
+
                     } /* end if */
-                    else
+                    else {
+
                        cache_ptr->entry_watched_for_removal = NULL;
+                    }
                 } /* end if */
             } /* end if */
         } /* end for loop scanning hash table */
@@ -5568,35 +6227,53 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
         old_ring_pel_len = cur_ring_pel_len;
         entry_ptr = cache_ptr->pel_head_ptr;
         cur_ring_pel_len = 0;
-        while(entry_ptr != NULL) {
+
+        while ( entry_ptr != NULL ) {
+
             HDassert(entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC);
             HDassert(entry_ptr->ring >= ring);
 
-            if(entry_ptr->ring == ring)
+            if ( entry_ptr->ring == ring ) {
+
                 cur_ring_pel_len++;
+            }
 
             entry_ptr = entry_ptr->next;
+
         } /* end while */
 
        /* Check if the number of pinned entries in the ring is positive, and
         * it is not declining.  Scream and die if so.
         */
-        if(cur_ring_pel_len > 0 && cur_ring_pel_len >= old_ring_pel_len) {
+        if ( ( cur_ring_pel_len > 0 ) && 
+             ( cur_ring_pel_len >= old_ring_pel_len ) ) {
+
             /* Don't error if allowed to have pinned entries remaining */
-            if(evict_flags)
+            if ( evict_flags ) {
+
                 HGOTO_DONE(TRUE)
+            }
 
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Pinned entry count not decreasing, cur_ring_pel_len = %d, old_ring_pel_len = %d, ring = %d", (int)cur_ring_pel_len, (int)old_ring_pel_len, (int)ring)
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                        "Pinned entry count not decreasing, cur_ring_pel_len = %d, old_ring_pel_len = %d, ring = %d", \
+                        (int)cur_ring_pel_len, \
+                        (int)old_ring_pel_len, (int)ring)
         } /* end if */
 
         HDassert(protected_entries == cache_ptr->pl_len);
 
-        if(protected_entries > 0 && protected_entries == cache_ptr->index_len)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Only protected entries left in cache, protected_entries = %d", (int)protected_entries)
+        if ( ( protected_entries > 0 ) && 
+             ( protected_entries == cache_ptr->index_len ) )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+               "Only protected entries left in cache, protected_entries = %d",\
+               (int)protected_entries)
+
     } /* main while loop */
 
     /* Invariants, after destroying all entries in the ring */
-    for(i = (int)H5C_RING_UNDEFINED; i <= (int)ring; i++) {
+    for ( i = (int)H5C_RING_UNDEFINED; i <= (int)ring; i++ ) {
+
         HDassert(cache_ptr->index_ring_len[i] == 0);
         HDassert(cache_ptr->index_ring_size[i] == (size_t)0);
         HDassert(cache_ptr->clean_index_ring_size[i] == (size_t)0);
@@ -5604,41 +6281,59 @@ H5C_flush_invalidate_ring(H5F_t * f, H5C_ring_t ring, unsigned flags)
 
         HDassert(cache_ptr->slist_ring_len[i] == 0);
         HDassert(cache_ptr->slist_ring_size[i] == (size_t)0);
+
     } /* end for */
 
     HDassert(protected_entries <= cache_ptr->pl_len);
 
-    if(protected_entries > 0)
-        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Cache has protected entries")
-    else if(cur_ring_pel_len > 0)
-        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't unpin all pinned entries in ring")
+    if ( protected_entries > 0 ) {
+
+        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                    "Cache has protected entries")
+
+    } else if ( cur_ring_pel_len > 0 ) {
+
+        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                    "Can't unpin all pinned entries in ring")
+    }
 
 done:
+
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5C_flush_invalidate_ring() */
 
 
 /*-------------------------------------------------------------------------
+ *
  * Function:    H5C__flush_ring
  *
- * Purpose:	Flush the entries contained in the specified cache and
- *		ring.  All entries in rings outside the specified ring
- *		must have been flushed on entry.
+ * Purpose:     Flush the entries contained in the specified cache and
+ *              ring.  All entries in rings outside the specified ring
+ *              must have been flushed on entry.
  *
- *		If the cache contains protected entries in the specified
- *		ring, the function will fail, as protected entries cannot
- *		be flushed.  However all unprotected entries in the target
- *		ring should be flushed before the function returns failure.
+ *              If the cache contains protected entries in the specified
+ *              ring, the function will fail, as protected entries cannot
+ *              be flushed.  However all unprotected entries in the target
+ *              ring should be flushed before the function returns failure.
  *
- *		If flush dependencies appear in the target ring, the
- *		function makes repeated passes through the slist flushing
- *		entries in flush dependency order.
+ *              If flush dependencies appear in the target ring, the
+ *              function makes repeated passes through the slist flushing
+ *              entries in flush dependency order.
  *
  * Return:      Non-negative on success/Negative on failure or if there was
- *		a request to flush all items and something was protected.
+ *              a request to flush all items and something was protected.
  *
  * Programmer:  John Mainzer
- *		9/1/15
+ *              9/1/15
+ *
+ * Changes:     A recent optimization turns off the slist unless a flush
+ *              is in progress.  This should not effect this function, as
+ *              it is only called during a flush.  Added an assertion to 
+ *              verify this.
+ *
+ *                                             JRM -- 5/6/20
+ *
  *
  *-------------------------------------------------------------------------
  */
@@ -5666,24 +6361,31 @@ H5C__flush_ring(H5F_t *f, H5C_ring_t ring, unsigned flags)
 
     HDassert(cache_ptr);
     HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);
+    HDassert(cache_ptr->slist_enabled);
     HDassert(cache_ptr->slist_ptr);
     HDassert((flags & H5C__FLUSH_INVALIDATE_FLAG) == 0);
     HDassert(ring > H5C_RING_UNDEFINED);
     HDassert(ring < H5C_RING_NTYPES);
 
 #if H5C_DO_EXTREME_SANITY_CHECKS
-    if((H5C_validate_protected_entry_list(cache_ptr) < 0) ||
-            (H5C_validate_pinned_entry_list(cache_ptr) < 0) ||
-            (H5C_validate_lru_list(cache_ptr) < 0))
-        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "an extreme sanity check failed on entry")
+    if ( ( H5C_validate_protected_entry_list(cache_ptr) < 0 ) ||
+         ( H5C_validate_pinned_entry_list(cache_ptr ) < 0 ) ||
+         ( H5C_validate_lru_list(cache_ptr) < 0 ) )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, 
+                    "an extreme sanity check failed on entry")
 #endif /* H5C_DO_EXTREME_SANITY_CHECKS */
 
     ignore_protected = ( (flags & H5C__FLUSH_IGNORE_PROTECTED_FLAG) != 0 );
     flush_marked_entries = ( (flags & H5C__FLUSH_MARKED_ENTRIES_FLAG) != 0 );
 
-    if(!flush_marked_entries)
-        for(i = (int)H5C_RING_UNDEFINED; i < (int)ring; i++)
-	    HDassert(cache_ptr->slist_ring_len[i] == 0);
+    if ( ! flush_marked_entries ) {
+
+        for ( i = (int)H5C_RING_UNDEFINED; i < (int)ring; i++ ) {
+
+            HDassert(cache_ptr->slist_ring_len[i] == 0);
+        }
+    }
 
     HDassert(cache_ptr->flush_in_progress);
 
@@ -5704,9 +6406,10 @@ H5C__flush_ring(H5F_t *f, H5C_ring_t ring, unsigned flags)
      */
     cache_ptr->slist_changed = FALSE;
 
-    while((cache_ptr->slist_ring_len[ring] > 0) &&
-	    (protected_entries == 0)  &&
-	    (flushed_entries_last_pass)) {
+    while ( ( cache_ptr->slist_ring_len[ring] > 0 ) &&
+            ( protected_entries == 0 )  &&
+            ( flushed_entries_last_pass ) ) {
+
         flushed_entries_last_pass = FALSE;
 
 #if H5C_DO_SANITY_CHECKS
@@ -5750,26 +6453,33 @@ H5C__flush_ring(H5F_t *f, H5C_ring_t ring, unsigned flags)
 
         restart_slist_scan = TRUE;
 
-        while((restart_slist_scan ) || (node_ptr != NULL)) {
-            if(restart_slist_scan) {
+        while ( ( restart_slist_scan ) || ( node_ptr != NULL ) ) {
+
+            if ( restart_slist_scan ) {
+
                 restart_slist_scan = FALSE;
 
                 /* Start at beginning of skip list */
                 node_ptr = H5SL_first(cache_ptr->slist_ptr);
 
-                if(node_ptr == NULL)
+                if ( node_ptr == NULL ) {
+
                     /* the slist is empty -- break out of inner loop */
                     break;
+                }
 
                 /* Get cache entry for this node */
                 next_entry_ptr = (H5C_cache_entry_t *)H5SL_item(node_ptr);
 
-                if(NULL == next_entry_ptr)
-                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "next_entry_ptr == NULL ?!?!")
+                if ( NULL == next_entry_ptr )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                                "next_entry_ptr == NULL ?!?!")
 
                 HDassert(next_entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC);
                 HDassert(next_entry_ptr->is_dirty);
                 HDassert(next_entry_ptr->in_slist);
+
             } /* end if */
 
             entry_ptr = next_entry_ptr;
@@ -5794,54 +6504,76 @@ H5C__flush_ring(H5F_t *f, H5C_ring_t ring, unsigned flags)
             HDassert(entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC);
             HDassert(entry_ptr->in_slist);
             HDassert(entry_ptr->is_dirty);
-            if(!flush_marked_entries || entry_ptr->flush_marker)
+
+            if ( ( ! flush_marked_entries ) || ( entry_ptr->flush_marker ) ) {
+
                 HDassert(entry_ptr->ring >= ring);
+            }
 
             /* Advance node pointer now, before we delete its target
              * from the slist.
              */
             node_ptr = H5SL_next(node_ptr);
-            if(node_ptr != NULL) {
+
+            if ( node_ptr != NULL ) {
+
                 next_entry_ptr = (H5C_cache_entry_t *)H5SL_item(node_ptr);
-                if(NULL == next_entry_ptr)
-                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "next_entry_ptr == NULL ?!?!")
+
+                if ( NULL == next_entry_ptr )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                                "next_entry_ptr == NULL ?!?!")
 
                 HDassert(next_entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC);
                 HDassert(next_entry_ptr->is_dirty);
                 HDassert(next_entry_ptr->in_slist);
 
-                if(!flush_marked_entries || next_entry_ptr->flush_marker)
+                if ( ! flush_marked_entries || next_entry_ptr->flush_marker ) {
+
                     HDassert(next_entry_ptr->ring >= ring);
+                }
 
                 HDassert(entry_ptr != next_entry_ptr);
+
             } /* end if */
-            else
+            else {
+
                 next_entry_ptr = NULL;
+            }
 
-            if((!flush_marked_entries || entry_ptr->flush_marker)
-                    && (!entry_ptr->flush_me_last ||
-                        (entry_ptr->flush_me_last
-                            && (cache_ptr->num_last_entries >= cache_ptr->slist_len
-                               || (flush_marked_entries && entry_ptr->flush_marker))))
-                    && (entry_ptr->flush_dep_nchildren == 0
-                        || entry_ptr->flush_dep_ndirty_children == 0)
-                    && entry_ptr->ring == ring) {
+            if ( ( ! flush_marked_entries || entry_ptr->flush_marker ) && 
+                 ( ( ! entry_ptr->flush_me_last ) ||
+                   ( ( entry_ptr->flush_me_last ) && 
+                     ( ( cache_ptr->num_last_entries >= cache_ptr->slist_len )||
+                       ( flush_marked_entries && entry_ptr->flush_marker ) )
+                   )
+                 ) && 
+                 ( ( entry_ptr->flush_dep_nchildren == 0 ) || 
+                   ( entry_ptr->flush_dep_ndirty_children == 0 ) ) && 
+                 ( entry_ptr->ring == ring ) ) {
 
                 HDassert(entry_ptr->flush_dep_nunser_children == 0);
 
-                if(entry_ptr->is_protected) {
+                if ( entry_ptr->is_protected ) {
+
                     /* we probably have major problems -- but lets
                      * flush everything we can before we decide
                      * whether to flag an error.
                      */
                     tried_to_flush_protected_entry = TRUE;
                     protected_entries++;
+
                 } /* end if */
                 else {
-                    if(H5C__flush_single_entry(f, entry_ptr, (flags | H5C__DURING_FLUSH_FLAG)) < 0)
-                        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't flush entry")
 
-                    if(cache_ptr->slist_changed) {
+                    if ( H5C__flush_single_entry(f, entry_ptr, 
+                                     (flags | H5C__DURING_FLUSH_FLAG)) < 0 )
+
+                        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                                    "Can't flush entry")
+
+                    if ( cache_ptr->slist_changed ) {
+
                         /* The slist has been modified by something
                          * other than the simple removal of the
                          * of the flushed entry after the flush.
@@ -5852,34 +6584,46 @@ H5C__flush_ring(H5F_t *f, H5C_ring_t ring, unsigned flags)
                         restart_slist_scan = TRUE;
                         cache_ptr->slist_changed = FALSE;
                         H5C__UPDATE_STATS_FOR_SLIST_SCAN_RESTART(cache_ptr)
+
                     } /* end if */
 
                     flushed_entries_last_pass = TRUE;
+
                 } /* end else */
             } /* end if */
         } /* while ( ( restart_slist_scan ) || ( node_ptr != NULL ) ) */
 
 #if H5C_DO_SANITY_CHECKS
         /* Verify that the slist size and length are as expected. */
-        HDassert((uint32_t)((int32_t)initial_slist_len + cache_ptr->slist_len_increase) == cache_ptr->slist_len);
-        HDassert((size_t)((ssize_t)initial_slist_size + cache_ptr->slist_size_increase) == cache_ptr->slist_size);
+        HDassert((uint32_t)((int32_t)initial_slist_len + \
+                    cache_ptr->slist_len_increase) == cache_ptr->slist_len);
+        HDassert((size_t)((ssize_t)initial_slist_size + \
+                    cache_ptr->slist_size_increase) == cache_ptr->slist_size);
 #endif /* H5C_DO_SANITY_CHECKS */
+
     } /* while */
 
     HDassert(protected_entries <= cache_ptr->pl_len);
 
-    if(((cache_ptr->pl_len > 0) && (!ignore_protected)) || (tried_to_flush_protected_entry))
-        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "cache has protected items")
+    if ( ( ( cache_ptr->pl_len > 0 ) && ( ! ignore_protected ) ) || 
+           ( tried_to_flush_protected_entry ) )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                    "cache has protected items")
 
 #if H5C_DO_SANITY_CHECKS
-    if(!flush_marked_entries) {
+    if ( ! flush_marked_entries ) {
+
         HDassert(cache_ptr->slist_ring_len[ring] == 0);
         HDassert(cache_ptr->slist_ring_size[ring] == 0);
+
     } /* end if */
 #endif /* H5C_DO_SANITY_CHECKS */
 
 done:
+
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5C__flush_ring() */
 
 
@@ -5888,53 +6632,110 @@ done:
  * Function:    H5C__flush_single_entry
  *
  * Purpose:     Flush or clear (and evict if requested) the cache entry
- *		with the specified address and type.  If the type is NULL,
- *		any unprotected entry at the specified address will be
- *		flushed (and possibly evicted).
+ *              with the specified address and type.  If the type is NULL,
+ *              any unprotected entry at the specified address will be
+ *              flushed (and possibly evicted).
  *
- *		Attempts to flush a protected entry will result in an
- *		error.
+ *              Attempts to flush a protected entry will result in an
+ *              error.
  *
- *		If the H5C__FLUSH_INVALIDATE_FLAG flag is set, the entry will
- *		be cleared and not flushed, and the call can't be part of a
+ *              If the H5C__FLUSH_INVALIDATE_FLAG flag is set, the entry will
+ *              be cleared and not flushed, and the call can't be part of a
  *              sequence of flushes.
  *
- *		If the caller knows the address of the skip list node at
- *		which the target entry resides, it can avoid a lookup
- *		by supplying that address in the tgt_node_ptr parameter.
- *		If this parameter is NULL, the function will do a skip list
- *		search for the entry instead.
- *
- *		The function does nothing silently if there is no entry
- *		at the supplied address, or if the entry found has the
- *		wrong type.
+ *              The function does nothing silently if there is no entry
+ *              at the supplied address, or if the entry found has the
+ *              wrong type.
  *
  * Return:      Non-negative on success/Negative on failure or if there was
- *		an attempt to flush a protected item.
+ *              an attempt to flush a protected item.
  *
  * Programmer:  John Mainzer, 5/5/04
  *
+ * Modifications:
+ *
+ *              JRM -- 7/21/04
+ *              Updated function for the addition of the hash table.
+ *
+ *              QAK -- 11/26/04
+ *              Updated function for the switch from TBBTs to skip lists.
+ *
+ *              JRM -- 1/6/05
+ *              Updated function to reset the flush_marker field.
+ *              Also replace references to H5F_FLUSH_INVALIDATE and
+ *              H5F_FLUSH_CLEAR_ONLY with references to
+ *              H5C__FLUSH_INVALIDATE_FLAG and H5C__FLUSH_CLEAR_ONLY_FLAG
+ *              respectively.
+ *
+ *              JRM -- 6/24/05
+ *              Added code to remove dirty entries from the slist after
+ *              they have been flushed.  Also added a sanity check that
+ *              will scream if we attempt a write when writes are
+ *              completely disabled.
+ *
+ *              JRM -- 7/5/05
+ *              Added code to call the new log_flush callback whenever
+ *              a dirty entry is written to disk.  Note that the callback
+ *              is not called if the H5C__FLUSH_CLEAR_ONLY_FLAG is set,
+ *              as there is no write to file in this case.
+ *
+ *              JRM -- 8/21/06
+ *              Added code maintaining the flush_in_progress and
+ *              destroy_in_progress fields in H5C_cache_entry_t.
+ *
+ *              Also added flush_flags parameter to the call to
+ *              type_ptr->flush() so that the flush routine can report
+ *              whether the entry has been resized or renamed.  Added
+ *              code using the flush_flags variable to detect the case
+ *              in which the target entry is resized during flush, and
+ *              update the caches data structures accordingly.
+ *
+ *              JRM -- 3/29/07
+ *              Added sanity checks on the new is_read_only and
+ *              ro_ref_count fields.
+ *
+ *              QAK -- 2/07/08
+ *              Separated "destroy entry" concept from "remove entry from
+ *              cache" concept, by adding the 'take_ownership' flag and
+ *              the "destroy_entry" variable.
+ *
+ *              JRM -- 11/5/08
+ *              Added call to H5C__UPDATE_INDEX_FOR_ENTRY_CLEAN() to
+ *              maintain the new clean_index_size and clean_index_size
+ *              fields of H5C_t.
+ *
+ *
+ *              Missing entries??
+ *
+ *
+ *              JRM -- 5/8/20
+ *              Updated sanity checks for the possibility that the slist 
+ *              is disabled.
+ *
+ *              Also updated main comment to conform more closely with 
+ *              the current state of the code.
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
 H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
 {
-    H5C_t *	     	cache_ptr;              /* Cache for file */
-    hbool_t		destroy;		/* external flag */
-    hbool_t		clear_only;		/* external flag */
-    hbool_t		free_file_space;	/* external flag */
-    hbool_t		take_ownership;		/* external flag */
-    hbool_t             del_from_slist_on_destroy;    /* external flag */
-    hbool_t		during_flush;		/* external flag */
-    hbool_t		write_entry;		/* internal flag */
-    hbool_t		destroy_entry;		/* internal flag */
-    hbool_t		generate_image;		/* internal flag */
-    hbool_t		update_page_buffer;	/* internal flag */
-    hbool_t		was_dirty;
-    hbool_t		suppress_image_entry_writes = FALSE;
-    hbool_t		suppress_image_entry_frees = FALSE;
-    haddr_t             entry_addr = HADDR_UNDEF;
-    herr_t		ret_value = SUCCEED;      /* Return value */
+    H5C_t *     cache_ptr;                      /* Cache for file */
+    hbool_t     destroy;                        /* external flag */
+    hbool_t     clear_only;                     /* external flag */
+    hbool_t     free_file_space;                /* external flag */
+    hbool_t     take_ownership;                 /* external flag */
+    hbool_t     del_from_slist_on_destroy;      /* external flag */
+    hbool_t     during_flush;                   /* external flag */
+    hbool_t     write_entry;                    /* internal flag */
+    hbool_t     destroy_entry;                  /* internal flag */
+    hbool_t     generate_image;                 /* internal flag */
+    hbool_t     update_page_buffer;             /* internal flag */
+    hbool_t     was_dirty;
+    hbool_t     suppress_image_entry_writes = FALSE;
+    hbool_t     suppress_image_entry_frees = FALSE;
+    haddr_t     entry_addr = HADDR_UNDEF;
+    herr_t      ret_value = SUCCEED;            /* Return value */
 
     FUNC_ENTER_PACKAGE
 
@@ -5948,30 +6749,39 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
     HDassert(entry_ptr->type);
 
     /* setup external flags from the flags parameter */
-    destroy                = ((flags & H5C__FLUSH_INVALIDATE_FLAG) != 0);
-    clear_only             = ((flags & H5C__FLUSH_CLEAR_ONLY_FLAG) != 0);
-    free_file_space        = ((flags & H5C__FREE_FILE_SPACE_FLAG) != 0);
-    take_ownership         = ((flags & H5C__TAKE_OWNERSHIP_FLAG) != 0);
-    del_from_slist_on_destroy = ((flags & H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG) != 0);
-    during_flush           = ((flags & H5C__DURING_FLUSH_FLAG) != 0);
-    generate_image         = ((flags & H5C__GENERATE_IMAGE_FLAG) != 0);
-    update_page_buffer     = ((flags & H5C__UPDATE_PAGE_BUFFER_FLAG) != 0);
+    destroy                   = ((flags & H5C__FLUSH_INVALIDATE_FLAG) != 0);
+    clear_only                = ((flags & H5C__FLUSH_CLEAR_ONLY_FLAG) != 0);
+    free_file_space           = ((flags & H5C__FREE_FILE_SPACE_FLAG) != 0);
+    take_ownership            = ((flags & H5C__TAKE_OWNERSHIP_FLAG) != 0);
+    del_from_slist_on_destroy = 
+                           ((flags & H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG) != 0);
+    during_flush              = ((flags & H5C__DURING_FLUSH_FLAG) != 0);
+    generate_image            = ((flags & H5C__GENERATE_IMAGE_FLAG) != 0);
+    update_page_buffer        = ((flags & H5C__UPDATE_PAGE_BUFFER_FLAG) != 0);
 
     /* Set the flag for destroying the entry, based on the 'take ownership'
      * and 'destroy' flags
      */
-    if(take_ownership)
+    if ( take_ownership ) {
+
         destroy_entry = FALSE;
-    else
+
+    } else {
+
         destroy_entry = destroy;
+    }
 
     /* we will write the entry to disk if it exists, is dirty, and if the
      * clear only flag is not set.
      */
-    if(entry_ptr->is_dirty && !clear_only)
+    if ( entry_ptr->is_dirty && !clear_only ) {
+
         write_entry = TRUE;
-    else
+
+    } else {
+
         write_entry = FALSE;
+    }
 
     /* if we have received close warning, and we have been instructed to
      * generate a metadata cache image, and we have actually constructed
@@ -5980,8 +6790,11 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
      * Set suppress_image_entry_writes to TRUE if indicated by the
      * image_ctl flags.
      */
-    if(cache_ptr->close_warning_received && cache_ptr->image_ctl.generate_image
-            && cache_ptr->num_entries_in_image > 0 && cache_ptr->image_entries) {
+    if ( ( cache_ptr->close_warning_received ) && 
+         ( cache_ptr->image_ctl.generate_image ) && 
+         ( cache_ptr->num_entries_in_image > 0 ) && 
+         ( cache_ptr->image_entries != NULL ) ) {
+
         /* Sanity checks */
         HDassert(entry_ptr->image_up_to_date || !(entry_ptr->include_in_image));
         HDassert(entry_ptr->image_ptr || !(entry_ptr->include_in_image));
@@ -5991,32 +6804,60 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
 
         suppress_image_entry_frees = TRUE;
 
-        if(cache_ptr->image_ctl.flags & H5C_CI__SUPRESS_ENTRY_WRITES)
+        if ( cache_ptr->image_ctl.flags & H5C_CI__SUPRESS_ENTRY_WRITES ) {
+
             suppress_image_entry_writes = TRUE;
+
+        } /* end if */
     } /* end if */
 
-    /* run initial sanity checks */
-#if H5C_DO_SANITY_CHECKS
-    if(entry_ptr->in_slist) {
-        HDassert(entry_ptr->is_dirty);
+    /* run initial sanity checks */ 
+#if H5C_DO_SANITY_CHECKS  
+    if ( cache_ptr->slist_enabled ) {
 
-        if((entry_ptr->flush_marker) && (!entry_ptr->is_dirty))
-            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "entry in slist failed sanity checks")
-    } /* end if */
-    else {
-        HDassert(!entry_ptr->is_dirty);
-        HDassert(!entry_ptr->flush_marker);
+        if ( entry_ptr->in_slist ) {
 
-        if((entry_ptr->is_dirty) || (entry_ptr->flush_marker))
-            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "entry failed sanity checks")
-    } /* end else */
+            HDassert(entry_ptr->is_dirty);
+
+            if ( ( entry_ptr->flush_marker ) && ( ! entry_ptr->is_dirty ) )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                            "entry in slist failed sanity checks")
+        } /* end if */
+        else {
+
+            HDassert(!entry_ptr->is_dirty);
+            HDassert(!entry_ptr->flush_marker);
+
+            if ( ( entry_ptr->is_dirty ) || ( entry_ptr->flush_marker ) )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                            "entry failed sanity checks")
+
+        } /* end else */
+    } else { /* slist is disabled */
+
+        HDassert( ! entry_ptr->in_slist );
+
+        if ( ! entry_ptr->is_dirty ) {
+
+            if ( entry_ptr->flush_marker )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                            "flush marked clean entry?")
+
+        }
+    }
 #endif /* H5C_DO_SANITY_CHECKS */
 
-    if(entry_ptr->is_protected) {
+    if ( entry_ptr->is_protected ) {
+
         HDassert(!entry_ptr->is_protected);
 
         /* Attempt to flush a protected entry -- scream and die. */
-        HGOTO_ERROR(H5E_CACHE, H5E_PROTECT, FAIL, "Attempt to flush a protected entry")
+        HGOTO_ERROR(H5E_CACHE, H5E_PROTECT, FAIL, \
+                    "Attempt to flush a protected entry")
+
     } /* end if */
 
     /* Set entry_ptr->flush_in_progress = TRUE and set
@@ -6035,24 +6876,36 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
      * been requested to generate an image.  In those cases, serialize the
      * entry.
      */
-    if(write_entry || generate_image) {
+    if ( write_entry || generate_image ) {
+
         HDassert(entry_ptr->is_dirty);
 
-        if(NULL == entry_ptr->image_ptr) {
-            if(NULL == (entry_ptr->image_ptr = H5MM_malloc(entry_ptr->size + H5C_IMAGE_EXTRA_SPACE)))
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "memory allocation failed for on disk image buffer")
+        if ( NULL == entry_ptr->image_ptr ) {
+
+            if ( NULL == (entry_ptr->image_ptr = 
+                       H5MM_malloc(entry_ptr->size + H5C_IMAGE_EXTRA_SPACE)) )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, \
+                           "memory allocation failed for on disk image buffer")
+
 #if H5C_DO_MEMORY_SANITY_CHECKS
-            H5MM_memcpy(((uint8_t *)entry_ptr->image_ptr) + entry_ptr->size, H5C_IMAGE_SANITY_VALUE, H5C_IMAGE_EXTRA_SPACE);
+            H5MM_memcpy(((uint8_t *)entry_ptr->image_ptr) + entry_ptr->size, 
+                        H5C_IMAGE_SANITY_VALUE, H5C_IMAGE_EXTRA_SPACE);
 #endif /* H5C_DO_MEMORY_SANITY_CHECKS */
+
         } /* end if */
 
-        if(!(entry_ptr->image_up_to_date)) {
+        if ( ! ( entry_ptr->image_up_to_date ) ) {
+
             /* Sanity check */
             HDassert(!entry_ptr->prefetched);
 
             /* Generate the entry's image */
-            if(H5C__generate_image(f, cache_ptr, entry_ptr) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "can't generate entry's image")
+            if ( H5C__generate_image(f, cache_ptr, entry_ptr) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, \
+                            "can't generate entry's image")
+
         } /* end if ( ! (entry_ptr->image_up_to_date) ) */
     } /* end if */
 
@@ -6062,12 +6915,16 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
      * in the entry's type, we silently skip the write.  This
      * flag should only be used in test code.
      */
-    if(write_entry) {
+    if ( write_entry ) {
+
         HDassert(entry_ptr->is_dirty);
 
 #if H5C_DO_SANITY_CHECKS
-        if(cache_ptr->check_write_permitted && !(cache_ptr->write_permitted))
-            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Write when writes are always forbidden!?!?!")
+        if ( ( cache_ptr->check_write_permitted ) && 
+             ( ! ( cache_ptr->write_permitted ) ) )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                        "Write when writes are always forbidden!?!?!")
 #endif /* H5C_DO_SANITY_CHECKS */
 
         /* Write the image to disk unless the write is suppressed.
@@ -6077,41 +6934,60 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
          * H5AC__CLASS_SKIP_WRITES is set in the entry's type.  This
          * flag should only be used in test code
          */
-        if((!suppress_image_entry_writes || !entry_ptr->include_in_image)
-                && (((entry_ptr->type->flags) & H5C__CLASS_SKIP_WRITES) == 0)) {
+        if ( ( ( ! suppress_image_entry_writes ) || 
+               ( ! entry_ptr->include_in_image ) ) && 
+             ( ( (entry_ptr->type->flags) & H5C__CLASS_SKIP_WRITES) == 0 ) ) {
+
             H5FD_mem_t mem_type = H5FD_MEM_DEFAULT;
 
 #ifdef H5_HAVE_PARALLEL
-            if(cache_ptr->coll_write_list) {
-                if(H5SL_insert(cache_ptr->coll_write_list, entry_ptr, &entry_ptr->addr) < 0)
-                    HGOTO_ERROR(H5E_CACHE, H5E_CANTINSERT, FAIL, "unable to insert skip list item")
+            if ( cache_ptr->coll_write_list ) {
+
+                if ( H5SL_insert(cache_ptr->coll_write_list, entry_ptr, 
+                                 &entry_ptr->addr) < 0 )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_CANTINSERT, FAIL, \
+                                "unable to insert skip list item")
             } /* end if */
             else
             {
 #endif /* H5_HAVE_PARALLEL */
 
-                if(entry_ptr->prefetched) {
+                if ( entry_ptr->prefetched ) {
+
                     HDassert(entry_ptr->type->id == H5AC_PREFETCHED_ENTRY_ID);
+
                     mem_type = cache_ptr->
                                class_table_ptr[entry_ptr->prefetch_type_id]->
                                mem_type;
                 } /* end if */
-                else
+                else {
+
                     mem_type = entry_ptr->type->mem_type;
+                }
+
+                if ( H5F_block_write(f, mem_type, entry_ptr->addr, 
+                                   entry_ptr->size, entry_ptr->image_ptr) < 0 )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                                "Can't write image to file")
 
-                if(H5F_block_write(f, mem_type, entry_ptr->addr, entry_ptr->size, entry_ptr->image_ptr) < 0)
-                    HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't write image to file")
 #ifdef H5_HAVE_PARALLEL
             }
 #endif /* H5_HAVE_PARALLEL */
+
         } /* end if */
 
         /* if the entry has a notify callback, notify it that we have
          * just flushed the entry.
          */
-        if(entry_ptr->type->notify &&
-                (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_AFTER_FLUSH, entry_ptr) < 0 )
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, "can't notify client of entry flush")
+        if ( ( entry_ptr->type->notify ) &&
+             ( (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_AFTER_FLUSH, 
+                                         entry_ptr) < 0 ) )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, \
+                        "can't notify client of entry flush")
+
     } /* if ( write_entry ) */
 
     /* At this point, all pre-serialize and serialize calls have been
@@ -6123,16 +6999,21 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
      */
 
     /* start by updating the statistics */
-    if(clear_only) {
+    if ( clear_only ) {
+
         /* only log a clear if the entry was dirty */
-        if(was_dirty) {
+        if ( was_dirty ) {
+
             H5C__UPDATE_STATS_FOR_CLEAR(cache_ptr, entry_ptr)
+
         } /* end if */
     } else if(write_entry) {
+
         HDassert(was_dirty);
 
         /* only log a flush if we actually wrote to disk */
         H5C__UPDATE_STATS_FOR_FLUSH(cache_ptr, entry_ptr)
+
     } /* end else if */
 
     /* Note that the algorithm below is (very) similar to the set of operations
@@ -6141,12 +7022,18 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
      */
 
     /* Update the cache internal data structures. */
-    if(destroy) {
+    if ( destroy ) {
+
         /* Sanity checks */
-        if(take_ownership)
+        if ( take_ownership ) {
+
             HDassert(!destroy_entry);
-        else
+
+        } else {
+
             HDassert(destroy_entry);
+        }
+
         HDassert(!entry_ptr->is_pinned);
 
         /* Update stats, while entry is still in the cache */
@@ -6156,8 +7043,12 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
          * to be removed from the cache, send a 'before eviction' notice while
          * the entry is still fully integrated in the cache.
          */
-        if(entry_ptr->type->notify && (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_BEFORE_EVICT, entry_ptr) < 0)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, "can't notify client about entry to evict")
+        if ( ( entry_ptr->type->notify ) && 
+             ( (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_BEFORE_EVICT, 
+                                         entry_ptr) < 0 ) )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, \
+                        "can't notify client about entry to evict")
 
         /* Update the cache internal data structures as appropriate
          * for a destroy.  Specifically:
@@ -6177,31 +7068,40 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
          */
         H5C__DELETE_FROM_INDEX(cache_ptr, entry_ptr, FAIL)
 
-        if(entry_ptr->in_slist && del_from_slist_on_destroy)
+        if ( ( entry_ptr->in_slist ) && ( del_from_slist_on_destroy ) ) {
+
             H5C__REMOVE_ENTRY_FROM_SLIST(cache_ptr, entry_ptr, during_flush)
+        }
 
 #ifdef H5_HAVE_PARALLEL
         /* Check for collective read access flag */
-        if(entry_ptr->coll_access) {
+        if ( entry_ptr->coll_access ) {
+
             entry_ptr->coll_access = FALSE;
+
             H5C__REMOVE_FROM_COLL_LIST(cache_ptr, entry_ptr, FAIL)
+
         } /* end if */
 #endif /* H5_HAVE_PARALLEL */
 
         H5C__UPDATE_RP_FOR_EVICTION(cache_ptr, entry_ptr, FAIL)
 
         /* Remove entry from tag list */
-        if(H5C__untag_entry(cache_ptr, entry_ptr) < 0)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTREMOVE, FAIL, "can't remove entry from tag list")
+        if ( H5C__untag_entry(cache_ptr, entry_ptr) < 0 )
 
-	/* verify that the entry is no longer part of any flush dependencies */
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTREMOVE, FAIL, \
+                        "can't remove entry from tag list")
+
+        /* verify that the entry is no longer part of any flush dependencies */
         HDassert(entry_ptr->flush_dep_nparents == 0);
-	HDassert(entry_ptr->flush_dep_nchildren == 0);
+        HDassert(entry_ptr->flush_dep_nchildren == 0);
+
     } /* end if */
     else {
+
         HDassert(clear_only || write_entry);
         HDassert(entry_ptr->is_dirty);
-        HDassert(entry_ptr->in_slist);
+        HDassert((!cache_ptr->slist_enabled) || (entry_ptr->in_slist));
 
         /* We are either doing a flush or a clear.
          *
@@ -6209,7 +7109,7 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
          * view of the replacement policy and the slist.
          * Hence no differentiation between them.
          *
-         * 					JRM -- 7/7/07
+         *                              JRM -- 7/7/07
          */
 
         H5C__UPDATE_RP_FOR_FLUSH(cache_ptr, entry_ptr, FAIL)
@@ -6225,20 +7125,34 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
         H5C__UPDATE_INDEX_FOR_ENTRY_CLEAN(cache_ptr, entry_ptr);
 
         /* Check for entry changing status and do notifications, etc. */
-        if(was_dirty) {
-            /* If the entry's type has a 'notify' callback send a 'entry cleaned'
-             * notice now that the entry is fully integrated into the cache.
+        if ( was_dirty ) {
+
+            /* If the entry's type has a 'notify' callback send a 
+             * 'entry cleaned' notice now that the entry is fully 
+             * integrated into the cache.
              */
-            if(entry_ptr->type->notify &&
-                    (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_ENTRY_CLEANED, entry_ptr) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, "can't notify client about entry dirty flag cleared")
+            if ( ( entry_ptr->type->notify ) &&
+                 ( (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_ENTRY_CLEANED, 
+                                             entry_ptr) < 0 ) )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, \
+                         "can't notify client about entry dirty flag cleared")
+
+            /* Propagate the clean flag up the flush dependency chain 
+             * if appropriate 
+             */
+            if ( entry_ptr->flush_dep_ndirty_children != 0 ) {
 
-            /* Propagate the clean flag up the flush dependency chain if appropriate */
-            if(entry_ptr->flush_dep_ndirty_children != 0)
                 HDassert(entry_ptr->flush_dep_ndirty_children == 0);
-            if(entry_ptr->flush_dep_nparents > 0)
-                if(H5C__mark_flush_dep_clean(entry_ptr) < 0)
-                    HGOTO_ERROR(H5E_CACHE, H5E_CANTMARKCLEAN, FAIL, "Can't propagate flush dep clean flag")
+            }
+
+            if ( entry_ptr->flush_dep_nparents > 0 ) {
+
+                if ( H5C__mark_flush_dep_clean(entry_ptr) < 0 )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_CANTMARKCLEAN, FAIL, \
+                                "Can't propagate flush dep clean flag")
+            }
         } /* end if */
     } /* end else */
 
@@ -6246,7 +7160,8 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
     entry_ptr->flush_in_progress = FALSE;
 
     /* capture the cache entry address for the log_flush call at the
-       end before the entry_ptr gets freed */
+     * end before the entry_ptr gets freed 
+     */
     entry_addr = entry_ptr->addr;
 
     /* Internal cache data structures should now be up to date, and
@@ -6254,7 +7169,8 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
      *
      * Now discard the entry if appropriate.
      */
-    if(destroy) {
+    if ( destroy ) {
+
         /* Sanity check */
         HDassert(0 == entry_ptr->flush_dep_nparents);
 
@@ -6265,10 +7181,14 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
          *
          * Otherwise, free the buffer if it exists.
          */
-        if(suppress_image_entry_frees && entry_ptr->include_in_image)
+        if ( suppress_image_entry_frees && entry_ptr->include_in_image ) {
+
             entry_ptr->image_ptr = NULL;
-        else if(entry_ptr->image_ptr != NULL)
+
+        } else if ( entry_ptr->image_ptr != NULL ) {
+
             entry_ptr->image_ptr = H5MM_xfree(entry_ptr->image_ptr);
+        }
 
         /* If the entry is not a prefetched entry, verify that the flush
          * dependency parents addresses array has been transferred.
@@ -6276,15 +7196,18 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
          * If the entry is prefetched, the free_isr routine will dispose of
          * the flush dependency parents addresses array if necessary.
          */
-        if(!entry_ptr->prefetched) {
+        if ( ! entry_ptr->prefetched ) {
+
             HDassert(0 == entry_ptr->fd_parent_count);
             HDassert(NULL == entry_ptr->fd_parent_addrs);
+
         } /* end if */
 
         /* Check whether we should free the space in the file that
          * the entry occupies
          */
-        if(free_file_space) {
+        if ( free_file_space ) {
+
             hsize_t fsf_size;
 
             /* Sanity checks */
@@ -6304,16 +7227,27 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
              * it to get the size of the block of file space to free.
              * Otherwise use entry_ptr->size.
              */
-            if(entry_ptr->type->fsf_size) {
-                if((entry_ptr->type->fsf_size)((void *)entry_ptr, &fsf_size) < 0)
-                    HGOTO_ERROR(H5E_CACHE, H5E_CANTFREE, FAIL, "unable to get file space free size")
+            if ( entry_ptr->type->fsf_size ) {
+
+                if ( (entry_ptr->type->fsf_size)((void *)entry_ptr, &fsf_size)
+                      < 0 )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_CANTFREE, FAIL, \
+                                "unable to get file space free size")
+
             } /* end if */
-            else    /* no file space free size callback -- use entry size */
+            else {   /* no file space free size callback -- use entry size */
+
                 fsf_size = entry_ptr->size;
+            }
 
             /* Release the space on disk */
-            if(H5MF_xfree(f, entry_ptr->type->mem_type, entry_ptr->addr, fsf_size) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTFREE, FAIL, "unable to free file space for cache entry")
+            if ( H5MF_xfree(f, entry_ptr->type->mem_type, 
+                            entry_ptr->addr, fsf_size) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTFREE, FAIL, \
+                            "unable to free file space for cache entry")
+
         } /* end if ( free_file_space ) */
 
         /* Reset the pointer to the cache the entry is within. -QAK */
@@ -6336,22 +7270,32 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
          */
         cache_ptr->entries_removed_counter++;
         cache_ptr->last_entry_removed_ptr = entry_ptr;
-        if(entry_ptr == cache_ptr->entry_watched_for_removal)
+
+        if ( entry_ptr == cache_ptr->entry_watched_for_removal ) {
+
             cache_ptr->entry_watched_for_removal = NULL;
+        }
 
         /* Check for actually destroying the entry in memory */
         /* (As opposed to taking ownership of it) */
-        if(destroy_entry) {
-            if(entry_ptr->is_dirty) {
+        if ( destroy_entry ) {
+
+            if ( entry_ptr->is_dirty ) {
+
                 /* Reset dirty flag */
                 entry_ptr->is_dirty = FALSE;
 
-                /* If the entry's type has a 'notify' callback send a 'entry cleaned'
-                 * notice now that the entry is fully integrated into the cache.
+                /* If the entry's type has a 'notify' callback send a 
+                 * 'entry cleaned' notice now that the entry is fully 
+                 * integrated into the cache.
                  */
-                if(entry_ptr->type->notify &&
-                        (entry_ptr->type->notify)(H5C_NOTIFY_ACTION_ENTRY_CLEANED, entry_ptr) < 0)
-                    HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, "can't notify client about entry dirty flag cleared")
+                if ( ( entry_ptr->type->notify ) &&
+                     ( (entry_ptr->type->notify)
+                           (H5C_NOTIFY_ACTION_ENTRY_CLEANED, entry_ptr) < 0 ) )
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, \
+                         "can't notify client about entry dirty flag cleared")
+
             } /* end if */
 
             /* we are about to discard the in core representation --
@@ -6363,10 +7307,14 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
             /* verify that the image has been freed */
             HDassert(entry_ptr->image_ptr == NULL);
 
-            if(entry_ptr->type->free_icr((void *)entry_ptr) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "free_icr callback failed")
+            if ( entry_ptr->type->free_icr((void *)entry_ptr) < 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                            "free_icr callback failed")
+
         }  /* end if */
         else {
+
             HDassert(take_ownership);
 
             /* client is taking ownership of the entry.
@@ -6374,33 +7322,50 @@ H5C__flush_single_entry(H5F_t *f, H5C_cache_entry_t *entry_ptr, unsigned flags)
              * unless the entry is re-inserted properly
              */
             entry_ptr->magic = H5C__H5C_CACHE_ENTRY_T_BAD_MAGIC;
+
         } /* end else */
     } /* if (destroy) */
 
     /* Check if we have to update the page buffer with cleared entries
      * so it doesn't go out of date
      */
-    if(update_page_buffer) {
+    if ( update_page_buffer ) {
+
         /* Sanity check */
         HDassert(!destroy);
         HDassert(entry_ptr->image_ptr);
 
-        if(f->shared->page_buf && f->shared->page_buf->page_size >= entry_ptr->size)
-            if(H5PB_update_entry(f->shared->page_buf, entry_ptr->addr, entry_ptr->size, entry_ptr->image_ptr) > 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Failed to update PB with metadata cache")
+        if ( ( f->shared->page_buf ) && 
+             ( f->shared->page_buf->page_size >= entry_ptr->size ) ) {
+
+            if ( H5PB_update_entry(f->shared->page_buf, entry_ptr->addr, 
+                                   entry_ptr->size, entry_ptr->image_ptr) > 0 )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                           "Failed to update PB with metadata cache")
+        } /* end if */
     } /* end if */
 
-    if(cache_ptr->log_flush)
-        if((cache_ptr->log_flush)(cache_ptr, entry_addr, was_dirty, flags) < 0)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "log_flush callback failed")
+    if ( cache_ptr->log_flush ) {
+
+        if ( (cache_ptr->log_flush)(cache_ptr, entry_addr, 
+                                    was_dirty, flags) < 0 )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                        "log_flush callback failed")
+
+    } /* end if */
 
 done:
+
     HDassert( ( ret_value != SUCCEED ) || ( destroy_entry ) ||
               ( ! entry_ptr->flush_in_progress ) );
+
     HDassert( ( ret_value != SUCCEED ) || ( destroy_entry ) ||
               ( take_ownership ) || ( ! entry_ptr->is_dirty ) );
 
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5C__flush_single_entry() */
 
 
@@ -7606,8 +8571,18 @@ H5C_entry_in_skip_list(H5C_t * cache_ptr, H5C_cache_entry_t *target_ptr)
  * Programmer:  Mike McGreevy
  *              November 3, 2010
  *
+ * Changes:     Modified function to setup the slist before calling 
+ *              H%C_flush_cache(), and take it down afterwards.  Note
+ *              that the slist need not be empty after the call to 
+ *              H5C_flush_cache() since we are only flushing marked 
+ *              entries.  Thus must set the clear_slist parameter 
+ *              of H5C_set_slist_enabled to TRUE.
+ *
+ *                                              JRM -- 5/6/20
+ *
  *-------------------------------------------------------------------------
  */
+
 herr_t
 H5C__flush_marked_entries(H5F_t * f)
 {
@@ -7618,12 +8593,31 @@ H5C__flush_marked_entries(H5F_t * f)
     /* Assertions */
     HDassert(f != NULL);
 
+
+    /* Enable the slist, as it is needed in the flush */
+    if ( H5C_set_slist_enabled(f->shared->cache, TRUE, FALSE) < 0 )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "set slist enabled failed")
+
+
     /* Flush all marked entries */
-    if(H5C_flush_cache(f, H5C__FLUSH_MARKED_ENTRIES_FLAG | H5C__FLUSH_IGNORE_PROTECTED_FLAG) < 0)
+    if ( H5C_flush_cache(f, H5C__FLUSH_MARKED_ENTRIES_FLAG | 
+                            H5C__FLUSH_IGNORE_PROTECTED_FLAG) < 0 )
+
         HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't flush cache")
 
+    /* Disable the slist.  Set the clear_slist parameter to TRUE
+     * since we called H5C_flush_cache() with the 
+     * H5C__FLUSH_MARKED_ENTRIES_FLAG.
+     */
+    if ( H5C_set_slist_enabled(f->shared->cache, FALSE, TRUE) < 0 )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "disable slist failed")
+
 done:
+
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5C__flush_marked_entries */
 
 
@@ -8479,7 +9473,7 @@ done:
  *
  * Purpose:     Serialize an entry and generate its image.
  *
- * Note:	This may cause the entry to be re-sized and/or moved in
+ * Note:        This may cause the entry to be re-sized and/or moved in
  *              the cache.
  *
  *              As we will not update the metadata cache's data structures
@@ -8493,14 +9487,18 @@ done:
  * Programmer:  Mohamad Chaarawi
  *              2/10/16
  *
+ * Changes:     Updated sanity checks for the possibility that the skip 
+ *              list is disabled.
+ *                                        JRM 5/16/20
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
 H5C__generate_image(H5F_t *f, H5C_t *cache_ptr, H5C_cache_entry_t *entry_ptr)
 {
-    haddr_t		new_addr = HADDR_UNDEF;
-    haddr_t		old_addr = HADDR_UNDEF;
-    size_t		new_len = 0;
+    haddr_t             new_addr = HADDR_UNDEF;
+    haddr_t             old_addr = HADDR_UNDEF;
+    size_t              new_len = 0;
     unsigned            serialize_flags = H5C__SERIALIZE_NO_FLAGS_SET;
     herr_t              ret_value = SUCCEED;
 
@@ -8521,16 +9519,24 @@ H5C__generate_image(H5F_t *f, H5C_t *cache_ptr, H5C_cache_entry_t *entry_ptr)
     old_addr = entry_ptr->addr;
 
     /* Call client's pre-serialize callback, if there's one */
-    if(entry_ptr->type->pre_serialize &&
-            (entry_ptr->type->pre_serialize)(f, (void *)entry_ptr,
-                entry_ptr->addr, entry_ptr->size, &new_addr, &new_len, &serialize_flags) < 0)
-        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "unable to pre-serialize entry")
+    if ( ( entry_ptr->type->pre_serialize ) &&
+         ( (entry_ptr->type->pre_serialize)(f, (void *)entry_ptr,
+                                            entry_ptr->addr, entry_ptr->size, 
+                                            &new_addr, &new_len, 
+                                            &serialize_flags) < 0 ) )
+
+        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                    "unable to pre-serialize entry")
 
     /* Check for any flags set in the pre-serialize callback */
-    if(serialize_flags != H5C__SERIALIZE_NO_FLAGS_SET) {
+    if ( serialize_flags != H5C__SERIALIZE_NO_FLAGS_SET ) {
+
         /* Check for unexpected flags from serialize callback */
-        if(serialize_flags & ~(H5C__SERIALIZE_RESIZED_FLAG | H5C__SERIALIZE_MOVED_FLAG))
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "unknown serialize flag(s)")
+        if ( serialize_flags & ~(H5C__SERIALIZE_RESIZED_FLAG | 
+                                 H5C__SERIALIZE_MOVED_FLAG) )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                        "unknown serialize flag(s)")
 
 #ifdef H5_HAVE_PARALLEL
         /* In the parallel case, resizes and moves in
@@ -8559,28 +9565,40 @@ H5C__generate_image(H5F_t *f, H5C_t *cache_ptr, H5C_cache_entry_t *entry_ptr)
          *     If that ceases to be the case, further
          *     tests will be necessary.
          */
-        if(cache_ptr->aux_ptr != NULL)
-            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "resize/move in serialize occurred in parallel case")
+        if ( cache_ptr->aux_ptr != NULL )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                        "resize/move in serialize occurred in parallel case")
 #endif
 
         /* If required, resize the buffer and update the entry and the cache
-         * data structures */
-        if(serialize_flags & H5C__SERIALIZE_RESIZED_FLAG) {
+         * data structures 
+         */
+        if ( serialize_flags & H5C__SERIALIZE_RESIZED_FLAG ) {
+
             /* Sanity check */
             HDassert(new_len > 0);
 
             /* Allocate a new image buffer */
-            if(NULL == (entry_ptr->image_ptr = H5MM_realloc(entry_ptr->image_ptr, new_len + H5C_IMAGE_EXTRA_SPACE)))
-                HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "memory allocation failed for on disk image buffer")
+            if ( NULL == (entry_ptr->image_ptr = 
+                          H5MM_realloc(entry_ptr->image_ptr, 
+                                       new_len + H5C_IMAGE_EXTRA_SPACE)) )
+
+                HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, \
+                        "memory allocation failed for on disk image buffer")
+
 #if H5C_DO_MEMORY_SANITY_CHECKS
-            H5MM_memcpy(((uint8_t *)entry_ptr->image_ptr) + new_len, H5C_IMAGE_SANITY_VALUE, H5C_IMAGE_EXTRA_SPACE);
+            H5MM_memcpy(((uint8_t *)entry_ptr->image_ptr) + new_len, 
+                        H5C_IMAGE_SANITY_VALUE, H5C_IMAGE_EXTRA_SPACE);
 #endif /* H5C_DO_MEMORY_SANITY_CHECKS */
 
             /* Update statistics for resizing the entry */
-            H5C__UPDATE_STATS_FOR_ENTRY_SIZE_CHANGE(cache_ptr, entry_ptr, new_len);
+            H5C__UPDATE_STATS_FOR_ENTRY_SIZE_CHANGE(cache_ptr, entry_ptr, \
+                                                    new_len);
 
             /* Update the hash table for the size change */
-            H5C__UPDATE_INDEX_FOR_SIZE_CHANGE(cache_ptr, entry_ptr->size, new_len, entry_ptr, !(entry_ptr->is_dirty));
+            H5C__UPDATE_INDEX_FOR_SIZE_CHANGE(cache_ptr, entry_ptr->size, \
+                                  new_len, entry_ptr, !(entry_ptr->is_dirty));
 
             /* The entry can't be protected since we are in the process of
              * flushing it.  Thus we must update the replacement policy data
@@ -8591,25 +9609,32 @@ H5C__generate_image(H5F_t *f, H5C_t *cache_ptr, H5C_cache_entry_t *entry_ptr)
 
             /* As we haven't updated the cache data structures for
              * for the flush or flush destroy yet, the entry should
-             * be in the slist.  Thus update it for the size change.
+             * be in the slist if the slist is enabled.  Since 
+             * H5C__UPDATE_SLIST_FOR_SIZE_CHANGE() is a no-op if the 
+             * slist is enabled, call it un-conditionally.
              */
             HDassert(entry_ptr->is_dirty);
-            HDassert(entry_ptr->in_slist);
-            H5C__UPDATE_SLIST_FOR_SIZE_CHANGE(cache_ptr, entry_ptr->size, new_len);
+            HDassert((entry_ptr->in_slist) || (!cache_ptr->slist_enabled));
+
+            H5C__UPDATE_SLIST_FOR_SIZE_CHANGE(cache_ptr, entry_ptr->size, \
+                                              new_len);
 
             /* Finally, update the entry for its new size */
             entry_ptr->size = new_len;
+
         } /* end if */
 
         /* If required, udate the entry and the cache data structures
          * for a move
          */
-        if(serialize_flags & H5C__SERIALIZE_MOVED_FLAG) {
+        if ( serialize_flags & H5C__SERIALIZE_MOVED_FLAG ) {
+
             /* Update stats and entries relocated counter */
             H5C__UPDATE_STATS_FOR_MOVE(cache_ptr, entry_ptr)
 
             /* We must update cache data structures for the change in address */
-            if(entry_ptr->addr == old_addr) {
+            if ( entry_ptr->addr == old_addr ) {
+
                 /* Delete the entry from the hash table and the slist */
                 H5C__DELETE_FROM_INDEX(cache_ptr, entry_ptr, FAIL);
                 H5C__REMOVE_ENTRY_FROM_SLIST(cache_ptr, entry_ptr, FALSE);
@@ -8620,18 +9645,26 @@ H5C__generate_image(H5F_t *f, H5C_t *cache_ptr, H5C_cache_entry_t *entry_ptr)
                 /* And then reinsert in the index and slist */
                 H5C__INSERT_IN_INDEX(cache_ptr, entry_ptr, FAIL);
                 H5C__INSERT_ENTRY_IN_SLIST(cache_ptr, entry_ptr, FAIL);
+
             } /* end if */
-            else /* move is already done for us -- just do sanity checks */
+            else { /* move is already done for us -- just do sanity checks */
+
                 HDassert(entry_ptr->addr == new_addr);
+            }
         } /* end if */
     } /* end if(serialize_flags != H5C__SERIALIZE_NO_FLAGS_SET) */
 
     /* Serialize object into buffer */
-    if(entry_ptr->type->serialize(f, entry_ptr->image_ptr, entry_ptr->size, (void *)entry_ptr) < 0)
+    if ( entry_ptr->type->serialize(f, entry_ptr->image_ptr, entry_ptr->size, 
+                                    (void *)entry_ptr) < 0 )
+
         HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "unable to serialize entry")
+
 #if H5C_DO_MEMORY_SANITY_CHECKS
-    HDassert(0 == HDmemcmp(((uint8_t *)entry_ptr->image_ptr) + entry_ptr->size, H5C_IMAGE_SANITY_VALUE, H5C_IMAGE_EXTRA_SPACE));
+    HDassert(0 == HDmemcmp(((uint8_t *)entry_ptr->image_ptr) + entry_ptr->size,\
+                            H5C_IMAGE_SANITY_VALUE, H5C_IMAGE_EXTRA_SPACE));
 #endif /* H5C_DO_MEMORY_SANITY_CHECKS */
+
     entry_ptr->image_up_to_date = TRUE;
 
     /* Propagate the fact that the entry is serialized up the
@@ -8641,9 +9674,14 @@ H5C__generate_image(H5F_t *f, H5C_t *cache_ptr, H5C_cache_entry_t *entry_ptr)
      * for flush dependency parents.
      */
     HDassert(entry_ptr->flush_dep_nunser_children == 0);
-    if(entry_ptr->flush_dep_nparents > 0)
-        if(H5C__mark_flush_dep_serialized(entry_ptr) < 0)
-            HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, "Can't propagate serialization status to fd parents")
+
+    if ( entry_ptr->flush_dep_nparents > 0 ) {
+
+        if ( H5C__mark_flush_dep_serialized(entry_ptr) < 0 )
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTNOTIFY, FAIL, \
+                         "Can't propagate serialization status to fd parents")
+    }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5Cdbg.c b/src/H5Cdbg.c
index d5599f2..775db4c 100644
--- a/src/H5Cdbg.c
+++ b/src/H5Cdbg.c
@@ -260,17 +260,24 @@ H5C_dump_cache_LRU(H5C_t *cache_ptr, const char *cache_name)
 
 
 /*-------------------------------------------------------------------------
+ *
  * Function:    H5C_dump_cache_skip_list
  *
  * Purpose:     Debugging routine that prints a summary of the contents of
- *		the skip list used by the metadata cache metadata cache to
- *		maintain an address sorted list of dirty entries.
+ *              the skip list used by the metadata cache metadata cache to
+ *              maintain an address sorted list of dirty entries.
  *
  * Return:      Non-negative on success/Negative on failure
  *
  * Programmer:  John Mainzer
  *              11/15/14
  *
+ * Changes:     Updated function for the slist_enabled field in H5C_t.
+ *              Recall that to minimize slist overhead, the slist is 
+ *              empty and not maintained if cache_ptr->slist_enabled is
+ *              false.
+ *                                             JRM -- 5/6/20
+ *
  *-------------------------------------------------------------------------
  */
 #ifndef NDEBUG
@@ -288,11 +295,16 @@ H5C_dump_cache_skip_list(H5C_t * cache_ptr, char * calling_fcn)
     HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);
     HDassert(calling_fcn != NULL);
 
-    HDfprintf(stdout, "\n\nDumping metadata cache skip list from %s.\n", calling_fcn);
+    HDfprintf(stdout, "\n\nDumping metadata cache skip list from %s.\n", 
+              calling_fcn);
+    HDfprintf(stdout, " slist enabled = %d.\n", 
+              (int)(cache_ptr->slist_enabled));
     HDfprintf(stdout, "	slist len = %u.\n", cache_ptr->slist_len);
-    HDfprintf(stdout, "	slist size = %lld.\n", (long long)(cache_ptr->slist_size));
+    HDfprintf(stdout, "	slist size = %lld.\n", 
+              (long long)(cache_ptr->slist_size));
 
     if(cache_ptr->slist_len > 0) {
+
         /* If we get this far, all entries in the cache are listed in the
          * skip list -- scan the skip list generating the desired output.
          */
@@ -300,13 +312,20 @@ H5C_dump_cache_skip_list(H5C_t * cache_ptr, char * calling_fcn)
                   "Num:    Addr:               Len: Prot/Pind: Dirty: Type:\n");
 
         i = 0;
+
         node_ptr = H5SL_first(cache_ptr->slist_ptr);
-        if(node_ptr != NULL)
+
+        if ( node_ptr != NULL ) {
+
             entry_ptr = (H5C_cache_entry_t *)H5SL_item(node_ptr);
-        else
+
+        } else {
+
             entry_ptr = NULL;
+        }
+
+        while ( entry_ptr != NULL ) {
 
-        while(entry_ptr != NULL) {
             HDassert( entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC );
 
             HDfprintf(stdout,
@@ -323,19 +342,27 @@ H5C_dump_cache_skip_list(H5C_t * cache_ptr, char * calling_fcn)
                       node_ptr, H5SL_item(node_ptr));
 
             /* increment node_ptr before we delete its target */
+
             node_ptr = H5SL_next(node_ptr);
-            if(node_ptr != NULL)
+
+            if ( node_ptr != NULL ) {
+
                 entry_ptr = (H5C_cache_entry_t *)H5SL_item(node_ptr);
-            else
+
+            } else {
+
                 entry_ptr = NULL;
+            }
 
             i++;
+
         } /* end while */
     } /* end if */
 
     HDfprintf(stdout, "\n\n");
 
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5C_dump_cache_skip_list() */
 #endif /* NDEBUG */
 
diff --git a/src/H5Cimage.c b/src/H5Cimage.c
index ee286d9..0373098 100644
--- a/src/H5Cimage.c
+++ b/src/H5Cimage.c
@@ -431,36 +431,40 @@ done:
  * Function:    H5C__deserialize_prefetched_entry()
  *
  * Purpose:     Deserialize the supplied prefetched entry entry, and return
- *		a pointer to the deserialized entry in *entry_ptr_ptr.
- *		If successful, remove the prefetched entry from the cache,
- *		and free it.  Insert the deserialized entry into the cache.
- *
- *		Note that the on disk image of the entry is not freed --
- *		a pointer to it is stored in the deserialized entries'
- *		image_ptr field, and its image_up_to_date field is set to
- *		TRUE unless the entry is dirtied by the deserialize call.
- *
- *		If the prefetched entry is a flush dependency child,
- *		destroy that flush dependency prior to calling the
- *		deserialize callback.  If appropriate, the flush dependency
- *		relationship will be recreated by the cache client.
- *
- *		If the prefetched entry is a flush dependency parent,
- *		destroy the flush dependency relationship with all its
- *		children.  As all these children must be prefetched entries,
- *		recreate these flush dependency relationships with
- *		deserialized entry after it is inserted in the cache.
- *
- *		Since deserializing a prefetched entry is semantically
- *		equivalent to a load, issue an entry loaded nofification
- *		if the notify callback is defined.
+ *              a pointer to the deserialized entry in *entry_ptr_ptr.
+ *              If successful, remove the prefetched entry from the cache,
+ *              and free it.  Insert the deserialized entry into the cache.
+ *
+ *              Note that the on disk image of the entry is not freed --
+ *              a pointer to it is stored in the deserialized entries'
+ *              image_ptr field, and its image_up_to_date field is set to
+ *              TRUE unless the entry is dirtied by the deserialize call.
+ *
+ *              If the prefetched entry is a flush dependency child,
+ *              destroy that flush dependency prior to calling the
+ *              deserialize callback.  If appropriate, the flush dependency
+ *              relationship will be recreated by the cache client.
+ *
+ *              If the prefetched entry is a flush dependency parent,
+ *              destroy the flush dependency relationship with all its
+ *              children.  As all these children must be prefetched entries,
+ *              recreate these flush dependency relationships with
+ *              deserialized entry after it is inserted in the cache.
+ *
+ *              Since deserializing a prefetched entry is semantically
+ *              equivalent to a load, issue an entry loaded nofification
+ *              if the notify callback is defined.
  *
  * Return:      SUCCEED on success, and FAIL on failure.
  *
- *		Note that *entry_ptr_ptr is undefined on failure.
+ *              Note that *entry_ptr_ptr is undefined on failure.
  *
  * Programmer:  John Mainzer, 8/10/15
  *
+ * Changes:     Updated sanity checks for possibility that the slist 
+ *              is disabled.
+ *                                            JRM -- 5/17/20
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
@@ -468,11 +472,11 @@ H5C__deserialize_prefetched_entry(H5F_t *f, H5C_t *cache_ptr,
     H5C_cache_entry_t **entry_ptr_ptr, const H5C_class_t *type,
     haddr_t addr, void *udata)
 {
-    hbool_t		dirty = FALSE;  /* Flag indicating whether thing was
+    hbool_t             dirty = FALSE;  /* Flag indicating whether thing was
                                          * dirtied during deserialize
                                          */
     size_t              len;            /* Size of image in file */
-    void *		thing = NULL;   /* Pointer to thing loaded */
+    void *              thing = NULL;   /* Pointer to thing loaded */
     H5C_cache_entry_t * pf_entry_ptr;   /* pointer to the prefetched entry   */
                                         /* supplied in *entry_ptr_ptr.       */
     H5C_cache_entry_t *	ds_entry_ptr;   /* Alias for thing loaded, as cache
@@ -484,8 +488,8 @@ H5C__deserialize_prefetched_entry(H5F_t *f, H5C_t *cache_ptr,
                                         /* the prefetched entry, or NULL if  */
                                         /* that array does not exist.        */
     unsigned            flush_flags = (H5C__FLUSH_INVALIDATE_FLAG |
-				       H5C__FLUSH_CLEAR_ONLY_FLAG);
-    int			i;
+                                       H5C__FLUSH_CLEAR_ONLY_FLAG);
+    int                 i;
     herr_t      	ret_value = SUCCEED;      /* Return value */
 
     FUNC_ENTER_PACKAGE
@@ -604,73 +608,73 @@ H5C__deserialize_prefetched_entry(H5F_t *f, H5C_t *cache_ptr,
 
     HDassert( ( dirty == FALSE ) || ( type->id == 5 || type->id == 6) );
 
-    ds_entry_ptr->magic                     	= H5C__H5C_CACHE_ENTRY_T_MAGIC;
-    ds_entry_ptr->cache_ptr                 	= f->shared->cache;
-    ds_entry_ptr->addr                      	= addr;
-    ds_entry_ptr->size                      	= len;
+    ds_entry_ptr->magic                     = H5C__H5C_CACHE_ENTRY_T_MAGIC;
+    ds_entry_ptr->cache_ptr                 = f->shared->cache;
+    ds_entry_ptr->addr                      = addr;
+    ds_entry_ptr->size                      = len;
     HDassert(ds_entry_ptr->size < H5C_MAX_ENTRY_SIZE);
-    ds_entry_ptr->image_ptr                 	= pf_entry_ptr->image_ptr;
-    ds_entry_ptr->image_up_to_date          	= !dirty;
-    ds_entry_ptr->type                      	= type;
-    ds_entry_ptr->is_dirty	            	= dirty | pf_entry_ptr->is_dirty;
-    ds_entry_ptr->dirtied                   	= FALSE;
-    ds_entry_ptr->is_protected              	= FALSE;
-    ds_entry_ptr->is_read_only              	= FALSE;
-    ds_entry_ptr->ro_ref_count              	= 0;
-    ds_entry_ptr->is_pinned                 	= FALSE;
-    ds_entry_ptr->in_slist                  	= FALSE;
-    ds_entry_ptr->flush_marker              	= FALSE;
+    ds_entry_ptr->image_ptr                 = pf_entry_ptr->image_ptr;
+    ds_entry_ptr->image_up_to_date          = !dirty;
+    ds_entry_ptr->type                      = type;
+    ds_entry_ptr->is_dirty	                = dirty | pf_entry_ptr->is_dirty;
+    ds_entry_ptr->dirtied                   = FALSE;
+    ds_entry_ptr->is_protected              = FALSE;
+    ds_entry_ptr->is_read_only              = FALSE;
+    ds_entry_ptr->ro_ref_count              = 0;
+    ds_entry_ptr->is_pinned                 = FALSE;
+    ds_entry_ptr->in_slist                  = FALSE;
+    ds_entry_ptr->flush_marker              = FALSE;
 #ifdef H5_HAVE_PARALLEL
-    ds_entry_ptr->clear_on_unprotect        	= FALSE;
-    ds_entry_ptr->flush_immediately         	= FALSE;
-    ds_entry_ptr->coll_access               	= FALSE;
+    ds_entry_ptr->clear_on_unprotect        = FALSE;
+    ds_entry_ptr->flush_immediately         = FALSE;
+    ds_entry_ptr->coll_access               = FALSE;
 #endif /* H5_HAVE_PARALLEL */
-    ds_entry_ptr->flush_in_progress         	= FALSE;
-    ds_entry_ptr->destroy_in_progress       	= FALSE;
+    ds_entry_ptr->flush_in_progress         = FALSE;
+    ds_entry_ptr->destroy_in_progress       = FALSE;
 
-    ds_entry_ptr->ring		            	= pf_entry_ptr->ring;
+    ds_entry_ptr->ring                      = pf_entry_ptr->ring;
 
     /* Initialize flush dependency height fields */
-    ds_entry_ptr->flush_dep_parent          	= NULL;
-    ds_entry_ptr->flush_dep_nparents        	= 0;
-    ds_entry_ptr->flush_dep_parent_nalloc   	= 0;
-    ds_entry_ptr->flush_dep_nchildren       	= 0;
-    ds_entry_ptr->flush_dep_ndirty_children 	= 0;
-    ds_entry_ptr->flush_dep_nunser_children 	= 0;
+    ds_entry_ptr->flush_dep_parent          = NULL;
+    ds_entry_ptr->flush_dep_nparents        = 0;
+    ds_entry_ptr->flush_dep_parent_nalloc   = 0;
+    ds_entry_ptr->flush_dep_nchildren       = 0;
+    ds_entry_ptr->flush_dep_ndirty_children = 0;
+    ds_entry_ptr->flush_dep_nunser_children = 0;
 
     /* Initialize fields supporting the hash table: */
-    ds_entry_ptr->ht_next                   	= NULL;
-    ds_entry_ptr->ht_prev                   	= NULL;
-    ds_entry_ptr->il_next                   	= NULL;
-    ds_entry_ptr->il_prev                   	= NULL;
+    ds_entry_ptr->ht_next                   = NULL;
+    ds_entry_ptr->ht_prev                   = NULL;
+    ds_entry_ptr->il_next                   = NULL;
+    ds_entry_ptr->il_prev                   = NULL;
 
     /* Initialize fields supporting replacement policies: */
-    ds_entry_ptr->next                      	= NULL;
-    ds_entry_ptr->prev                      	= NULL;
+    ds_entry_ptr->next                      = NULL;
+    ds_entry_ptr->prev                      = NULL;
 #if H5C_MAINTAIN_CLEAN_AND_DIRTY_LRU_LISTS
-    ds_entry_ptr->aux_next                  	= NULL;
-    ds_entry_ptr->aux_prev                  	= NULL;
+    ds_entry_ptr->aux_next                  = NULL;
+    ds_entry_ptr->aux_prev                  = NULL;
 #endif /* H5C_MAINTAIN_CLEAN_AND_DIRTY_LRU_LISTS */
 #ifdef H5_HAVE_PARALLEL
-    pf_entry_ptr->coll_next                 	= NULL;
-    pf_entry_ptr->coll_prev                 	= NULL;
+    pf_entry_ptr->coll_next                 = NULL;
+    pf_entry_ptr->coll_prev                 = NULL;
 #endif /* H5_HAVE_PARALLEL */
 
     /* Initialize cache image related fields */
-    ds_entry_ptr->include_in_image          	= FALSE;
-    ds_entry_ptr->lru_rank	            	= 0;
-    ds_entry_ptr->image_dirty	            	= FALSE;
-    ds_entry_ptr->fd_parent_count           	= 0;
-    ds_entry_ptr->fd_parent_addrs           	= NULL;
-    ds_entry_ptr->fd_child_count            	= pf_entry_ptr->fd_child_count;
-    ds_entry_ptr->fd_dirty_child_count      	= 0;
-    ds_entry_ptr->image_fd_height           	= 0;
-    ds_entry_ptr->prefetched	            	= FALSE;
-    ds_entry_ptr->prefetch_type_id          	= 0;
-    ds_entry_ptr->age		          	= 0;
-    ds_entry_ptr->prefetched_dirty              = pf_entry_ptr->prefetched_dirty;
+    ds_entry_ptr->include_in_image          = FALSE;
+    ds_entry_ptr->lru_rank	                = 0;
+    ds_entry_ptr->image_dirty	             = FALSE;
+    ds_entry_ptr->fd_parent_count           = 0;
+    ds_entry_ptr->fd_parent_addrs           = NULL;
+    ds_entry_ptr->fd_child_count            = pf_entry_ptr->fd_child_count;
+    ds_entry_ptr->fd_dirty_child_count      = 0;
+    ds_entry_ptr->image_fd_height           = 0;
+    ds_entry_ptr->prefetched	              = FALSE;
+    ds_entry_ptr->prefetch_type_id          = 0;
+    ds_entry_ptr->age                       = 0;
+    ds_entry_ptr->prefetched_dirty          = pf_entry_ptr->prefetched_dirty;
 #ifndef NDEBUG  /* debugging field */
-    ds_entry_ptr->serialization_count           = 0;
+    ds_entry_ptr->serialization_count       = 0;
 #endif /* NDEBUG */
 
     H5C__RESET_CACHE_ENTRY_STATS(ds_entry_ptr);
@@ -694,15 +698,20 @@ H5C__deserialize_prefetched_entry(H5F_t *f, H5C_t *cache_ptr,
      *
      *  1) Set pf_entry_ptr->image_ptr to NULL.  Since we have already
      *     transferred the buffer containing the image to *ds_entry_ptr,
-     *	   this is not a memory leak.
+     *     this is not a memory leak.
      *
      *  2) Call H5C__flush_single_entry() with the H5C__FLUSH_INVALIDATE_FLAG
      *     and H5C__FLUSH_CLEAR_ONLY_FLAG flags set.
      */
     pf_entry_ptr->image_ptr = NULL;
-    if(pf_entry_ptr->is_dirty) {
-        HDassert(pf_entry_ptr->in_slist);
+
+    if ( pf_entry_ptr->is_dirty ) {
+
+        HDassert(((cache_ptr->slist_enabled) && (pf_entry_ptr->in_slist)) || \
+                 ((!cache_ptr->slist_enabled) && (!pf_entry_ptr->in_slist)));
+
         flush_flags |= H5C__DEL_FROM_SLIST_ON_DESTROY_FLAG;
+
     } /* end if */
 
     if(H5C__flush_single_entry(f, pf_entry_ptr, flush_flags) < 0)
diff --git a/src/H5Cmpio.c b/src/H5Cmpio.c
index 2f2f3fc..3579bc2 100644
--- a/src/H5Cmpio.c
+++ b/src/H5Cmpio.c
@@ -18,7 +18,7 @@
  *              Quincey Koziol
  *
  * Purpose:     Functions in this file implement support for parallel I/O for
- *              generic cache code.
+ *		generic cache code.
  *
  *-------------------------------------------------------------------------
  */
@@ -28,7 +28,7 @@
 /****************/
 
 #include "H5Cmodule.h"          /* This source code file is part of the H5C module */
-#define H5F_FRIEND        /*suppress error about including H5Fpkg      */
+#define H5F_FRIEND		/*suppress error about including H5Fpkg	  */
 
 
 /***********/
@@ -114,9 +114,9 @@ static herr_t H5C__flush_candidates_in_ring(H5F_t *f, H5C_ring_t ring,
  *
  *              We construct the table as follows.  Let:
  *
- *                  n = num_candidates / mpi_size;
+ *                      n = num_candidates / mpi_size;
  *
- *                  m = num_candidates % mpi_size;
+ *                      m = num_candidates % mpi_size;
  *
  *              Now allocate an array of integers of length mpi_size + 1,
  *              and call this array candidate_assignment_table.
@@ -136,10 +136,10 @@ static herr_t H5C__flush_candidates_in_ring(H5F_t *f, H5C_ring_t ring,
  *              Once the table is constructed, we determine the first and
  *              last entry this process is to flush as follows:
  *
- *                  first_entry_to_flush = candidate_assignment_table[mpi_rank]
+ *              first_entry_to_flush = candidate_assignment_table[mpi_rank]
  *
  *              last_entry_to_flush =
- *                  candidate_assignment_table[mpi_rank + 1] - 1;
+ *                      candidate_assignment_table[mpi_rank + 1] - 1;
  *
  *              With these values determined, we simply scan through the
  *              candidate list, marking all entries in the range
@@ -163,6 +163,10 @@ static herr_t H5C__flush_candidates_in_ring(H5F_t *f, H5C_ring_t ring,
  * Programmer:  John Mainzer
  *              3/17/10
  *
+ * Changes:     Updated sanity checks to allow for the possibility that 
+ *              the slist is disabled.
+ *                                               JRM -- 8/3/20
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
@@ -185,12 +189,15 @@ H5C_apply_candidate_list(H5F_t * f,
     unsigned            entries_to_clear[H5C_RING_NTYPES];
     haddr_t             addr;
     H5C_cache_entry_t * entry_ptr = NULL;
+
 #if H5C_DO_SANITY_CHECKS
     haddr_t             last_addr;
 #endif /* H5C_DO_SANITY_CHECKS */
+
 #if H5C_APPLY_CANDIDATE_LIST__DEBUG
     char                tbl_buf[1024];
 #endif /* H5C_APPLY_CANDIDATE_LIST__DEBUG */
+
     unsigned            u;                      /* Local index variable */
     herr_t              ret_value = SUCCEED;    /* Return value */
 
@@ -200,7 +207,8 @@ H5C_apply_candidate_list(H5F_t * f,
     HDassert(cache_ptr != NULL);
     HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);
     HDassert(num_candidates > 0);
-    HDassert(num_candidates <= cache_ptr->slist_len);
+    HDassert( ( ! cache_ptr->slist_enabled ) ||
+              ( num_candidates <= cache_ptr->slist_len ));
     HDassert(candidates_list_ptr != NULL);
     HDassert(0 <= mpi_rank);
     HDassert(mpi_rank < mpi_size);
@@ -409,6 +417,7 @@ done:
 
 
 /*-------------------------------------------------------------------------
+ *
  * Function:    H5C_construct_candidate_list__clean_cache
  *
  * Purpose:     Construct the list of entries that should be flushed to
@@ -424,6 +433,16 @@ done:
  * Programmer:  John Mainzer
  *              3/17/10
  *
+ * Changes:     With the slist optimization, the slist is not maintained
+ *              unless a flush is in progress.  Thus we can not longer use
+ *              cache_ptr->slist_size to determine the total size of 
+ *              the entries we must insert in the candidate list.
+ *
+ *              To address this, we now use cache_ptr->dirty_index_size
+ *              instead.  
+ *
+ *                                              JRM -- 7/27/20
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
@@ -437,60 +456,82 @@ H5C_construct_candidate_list__clean_cache(H5C_t * cache_ptr)
     HDassert( cache_ptr != NULL );
     HDassert( cache_ptr->magic == H5C__H5C_T_MAGIC );
 
-    /* As a sanity check, set space needed to the size of the skip list.
-     * This should be the sum total of the sizes of all the dirty entries
-     * in the metadata cache.
+    /* As a sanity check, set space needed to the dirty_index_size.  This
+     * should be the sum total of the sizes of all the dirty entries
+     * in the metadata cache.  Note that if the slist is enabled, 
+     * cache_ptr->slist_size should equal cache_ptr->dirty_index_size.
      */
-    space_needed = cache_ptr->slist_size;
+    space_needed = cache_ptr->dirty_index_size;
+
+    HDassert( ( ! cache_ptr->slist_enabled ) ||
+              ( space_needed == cache_ptr->slist_size ) );
+
 
     /* Recall that while we shouldn't have any protected entries at this
      * point, it is possible that some dirty entries may reside on the
      * pinned list at this point.
      */
-    HDassert( cache_ptr->slist_size <=
+    HDassert( cache_ptr->dirty_index_size <=
               (cache_ptr->dLRU_list_size + cache_ptr->pel_size) );
-    HDassert( cache_ptr->slist_len  <=
-              (cache_ptr->dLRU_list_len + cache_ptr->pel_len) );
+    HDassert( ( ! cache_ptr->slist_enabled ) ||
+              ( cache_ptr->slist_len  <=
+                (cache_ptr->dLRU_list_len + cache_ptr->pel_len) ) );
+
 
     if(space_needed > 0) { /* we have work to do */
+
         H5C_cache_entry_t *entry_ptr;
         unsigned nominated_entries_count = 0;
         size_t  nominated_entries_size = 0;
-        haddr_t nominated_addr;
+        haddr_t	nominated_addr;
 
-        HDassert( cache_ptr->slist_len > 0 );
+        HDassert( ( ! cache_ptr->slist_enabled ) ||
+                  ( cache_ptr->slist_len > 0 ) );
 
         /* Scan the dirty LRU list from tail forward and nominate sufficient
          * entries to free up the necessary space.
          */
         entry_ptr = cache_ptr->dLRU_tail_ptr;
-        while((nominated_entries_size < space_needed) &&
-                (nominated_entries_count < cache_ptr->slist_len) &&
-                (entry_ptr != NULL)) {
+
+        while ( ( nominated_entries_size < space_needed ) &&
+                ( ( ! cache_ptr->slist_enabled ) ||
+                  ( nominated_entries_count < cache_ptr->slist_len ) ) &&
+                ( entry_ptr != NULL ) ) {
+
             HDassert( ! (entry_ptr->is_protected) );
             HDassert( ! (entry_ptr->is_read_only) );
             HDassert( entry_ptr->ro_ref_count == 0 );
             HDassert( entry_ptr->is_dirty );
-            HDassert( entry_ptr->in_slist );
+            HDassert( ( ! cache_ptr->slist_enabled ) ||
+                      ( entry_ptr->in_slist ) );
 
             nominated_addr = entry_ptr->addr;
+
             if(H5AC_add_candidate((H5AC_t *)cache_ptr, nominated_addr) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "H5AC_add_candidate() failed")
+
+                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                            "H5AC_add_candidate() failed")
 
             nominated_entries_size += entry_ptr->size;
             nominated_entries_count++;
             entry_ptr = entry_ptr->aux_prev;
+
         } /* end while */
+
         HDassert( entry_ptr == NULL );
 
         /* it is possible that there are some dirty entries on the
          * protected entry list as well -- scan it too if necessary
          */
         entry_ptr = cache_ptr->pel_head_ptr;
-        while((nominated_entries_size < space_needed) &&
-                (nominated_entries_count < cache_ptr->slist_len) &&
-                (entry_ptr != NULL)) {
+
+        while ( ( nominated_entries_size < space_needed ) &&
+                ( ( ! cache_ptr->slist_enabled ) ||
+                  ( nominated_entries_count < cache_ptr->slist_len ) ) &&
+                ( entry_ptr != NULL ) ) {
+
             if(entry_ptr->is_dirty) {
+
                 HDassert( ! (entry_ptr->is_protected) );
                 HDassert( ! (entry_ptr->is_read_only) );
                 HDassert( entry_ptr->ro_ref_count == 0 );
@@ -498,22 +539,31 @@ H5C_construct_candidate_list__clean_cache(H5C_t * cache_ptr)
                 HDassert( entry_ptr->in_slist );
 
                 nominated_addr = entry_ptr->addr;
+
                 if(H5AC_add_candidate((H5AC_t *)cache_ptr, nominated_addr) < 0)
-                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "H5AC_add_candidate() failed")
+
+                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                                "H5AC_add_candidate() failed")
 
                 nominated_entries_size += entry_ptr->size;
                 nominated_entries_count++;
+
             } /* end if */
 
             entry_ptr = entry_ptr->next;
+
         } /* end while */
 
-        HDassert( nominated_entries_count == cache_ptr->slist_len );
+        HDassert( ( ! cache_ptr->slist_enabled ) ||
+                  ( nominated_entries_count == cache_ptr->slist_len ) );
         HDassert( nominated_entries_size == space_needed );
+
     } /* end if */
 
 done:
+
     FUNC_LEAVE_NOAPI(ret_value)
+
 } /* H5C_construct_candidate_list__clean_cache() */
 
 
@@ -533,6 +583,12 @@ done:
  * Programmer:  John Mainzer
  *              3/17/10
  *
+ * Changes:     With the slist optimization, the slist is not maintained
+ *              unless a flush is in progress.  Updated sanity checks to 
+ *              reflect this.
+ *
+ *                                              JRM -- 7/27/20
+ *
  *-------------------------------------------------------------------------
  */
 herr_t
@@ -550,54 +606,77 @@ H5C_construct_candidate_list__min_clean(H5C_t * cache_ptr)
      * cache back within its min clean constraints.
      */
     if(cache_ptr->max_cache_size > cache_ptr->index_size) {
-        if(((cache_ptr->max_cache_size - cache_ptr->index_size) +
-               cache_ptr->cLRU_list_size) >= cache_ptr->min_clean_size)
+
+        if ( ( (cache_ptr->max_cache_size - cache_ptr->index_size) +
+                cache_ptr->cLRU_list_size) >= cache_ptr->min_clean_size ) {
+ 
             space_needed = 0;
-        else
+
+        } else {
+
             space_needed = cache_ptr->min_clean_size -
                 ((cache_ptr->max_cache_size - cache_ptr->index_size) +
                  cache_ptr->cLRU_list_size);
+        }
     } /* end if */
     else {
-        if(cache_ptr->min_clean_size <= cache_ptr->cLRU_list_size)
+
+        if(cache_ptr->min_clean_size <= cache_ptr->cLRU_list_size) {
+
            space_needed = 0;
-        else
+
+        } else {
+
             space_needed = cache_ptr->min_clean_size -
                            cache_ptr->cLRU_list_size;
+        }
     } /* end else */
 
     if(space_needed > 0) { /* we have work to do */
+
         H5C_cache_entry_t *entry_ptr;
         unsigned nominated_entries_count = 0;
         size_t nominated_entries_size = 0;
 
-        HDassert( cache_ptr->slist_len > 0 );
+        HDassert( ( ! cache_ptr->slist_enabled ) || 
+                  ( cache_ptr->slist_len > 0 ) );
 
         /* Scan the dirty LRU list from tail forward and nominate sufficient
          * entries to free up the necessary space.
          */
         entry_ptr = cache_ptr->dLRU_tail_ptr;
-        while((nominated_entries_size < space_needed) &&
-                (nominated_entries_count < cache_ptr->slist_len) &&
-                (entry_ptr != NULL) &&
-                (!entry_ptr->flush_me_last)) {
-            haddr_t nominated_addr;
+
+        while ( ( nominated_entries_size < space_needed ) &&
+                ( ( ! cache_ptr->slist_enabled ) ||
+                  ( nominated_entries_count < cache_ptr->slist_len ) ) &&
+                ( entry_ptr != NULL ) &&
+                ( ! entry_ptr->flush_me_last ) ) {
+
+            haddr_t		nominated_addr;
 
             HDassert( ! (entry_ptr->is_protected) );
             HDassert( ! (entry_ptr->is_read_only) );
             HDassert( entry_ptr->ro_ref_count == 0 );
             HDassert( entry_ptr->is_dirty );
-            HDassert( entry_ptr->in_slist );
+            HDassert( ( ! cache_ptr->slist_enabled ) || 
+                      ( entry_ptr->in_slist ) );
 
             nominated_addr = entry_ptr->addr;
+
             if(H5AC_add_candidate((H5AC_t *)cache_ptr, nominated_addr) < 0)
-                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "H5AC_add_candidate() failed")
+
+                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, \
+                            "H5AC_add_candidate() failed")
 
             nominated_entries_size += entry_ptr->size;
             nominated_entries_count++;
             entry_ptr = entry_ptr->aux_prev;
+
         } /* end while */
-        HDassert( nominated_entries_count <= cache_ptr->slist_len );
+
+        HDassert( ( ! cache_ptr->slist_enabled ) ||
+                  ( nominated_entries_count <= cache_ptr->slist_len ) );
+        HDassert( nominated_entries_size <= cache_ptr->dirty_index_size );
         HDassert( nominated_entries_size >= space_needed );
     } /* end if */
 
@@ -768,7 +847,7 @@ H5C_mark_entries_as_clean(H5F_t *  f,
      * of the pre_serialize / serialize routines, this may
      * cease to be the case -- requiring a review of this
      * point.
-     *                    JRM -- 4/7/15
+     *                                  JRM -- 4/7/15
      */
     entries_cleared = 0;
     entries_examined = 0;
@@ -872,9 +951,9 @@ done:
 herr_t
 H5C_clear_coll_entries(H5C_t *cache_ptr, hbool_t partial)
 {
-    uint32_t                clear_cnt;
-    H5C_cache_entry_t *     entry_ptr = NULL;
-    herr_t                  ret_value = SUCCEED;
+    uint32_t            clear_cnt;
+    H5C_cache_entry_t * entry_ptr = NULL;
+    herr_t              ret_value = SUCCEED;
 
     FUNC_ENTER_NOAPI_NOINIT
 
@@ -1123,17 +1202,17 @@ H5C__flush_candidate_entries(H5F_t *f, unsigned entries_to_flush[H5C_RING_NTYPES
     unsigned entries_to_clear[H5C_RING_NTYPES])
 {
 #if H5C_DO_SANITY_CHECKS
-    int             i;
-    uint32_t        index_len = 0;
-    size_t          index_size = (size_t)0;
-    size_t          clean_index_size = (size_t)0;
-    size_t          dirty_index_size = (size_t)0;
-    size_t          slist_size = (size_t)0;
-    uint32_t        slist_len = 0;
+    int                 i;
+    uint32_t            index_len = 0;
+    size_t              index_size = (size_t)0;
+    size_t              clean_index_size = (size_t)0;
+    size_t              dirty_index_size = (size_t)0;
+    size_t              slist_size = (size_t)0;
+    uint32_t            slist_len = 0;
 #endif /* H5C_DO_SANITY_CHECKS */
-    H5C_ring_t      ring;
+    H5C_ring_t          ring;
     H5C_t             * cache_ptr;
-    herr_t          ret_value = SUCCEED;
+    herr_t              ret_value = SUCCEED;
 
     FUNC_ENTER_STATIC
 
diff --git a/src/H5Cpkg.h b/src/H5Cpkg.h
index 779f289..79ebd9e 100644
--- a/src/H5Cpkg.h
+++ b/src/H5Cpkg.h
@@ -47,13 +47,22 @@
 /* Number of epoch markers active */
 #define H5C__MAX_EPOCH_MARKERS                  10
 
+
 /* Cache configuration settings */
 #define H5C__HASH_TABLE_LEN     (64 * 1024) /* must be a power of 2 */
 #define H5C__H5C_T_MAGIC	0x005CAC0E
 
+
 /* Initial allocated size of the "flush_dep_parent" array */
 #define H5C_FLUSH_DEP_PARENT_INIT 8
 
+
+/* Set to TRUE to enable the slist optimization.  If this field is TRUE,
+ * the slist is disabled whenever a flush is not in progress.
+ */
+#define H5C__SLIST_OPT_ENABLED                  TRUE
+
+
 /****************************************************************************
  *
  * We maintain doubly linked lists of instances of H5C_cache_entry_t for a
@@ -1568,49 +1577,82 @@ if ( ( (cache_ptr)->index_size !=                                           \
  *		Added code to maintain the cache_ptr->slist_ring_len
  *		and cache_ptr->slist_ring_size arrays.
  *
+ *              JRM -- 4/29/20
+ *              Reworked macro to support the slist_enabled field 
+ *              of H5C_t.  If slist_enabled == TRUE, the macro 
+ *              functions as before.  Otherwise, the macro is a no-op,
+ *              and the slist must be empty.
+ *
  *-------------------------------------------------------------------------
  */
 
+/* NOTE:  The H5C__INSERT_ENTRY_IN_SLIST() macro is set up so that 
+ *        
+ *            H5C_DO_SANITY_CHECKS 
+ *
+ *        and 
+ *
+ *            H5C_DO_SLIST_SANITY_CHECKS 
+ *
+ *        can be selected independantly.  This is easy to miss as the 
+ *        two #defines are easy to confuse.
+ */
+
 #if H5C_DO_SLIST_SANITY_CHECKS
+
 #define ENTRY_IN_SLIST(cache_ptr, entry_ptr) \
     H5C_entry_in_skip_list((cache_ptr), (entry_ptr))
+
 #else /* H5C_DO_SLIST_SANITY_CHECKS */
+
 #define ENTRY_IN_SLIST(cache_ptr, entry_ptr) FALSE
+
 #endif /* H5C_DO_SLIST_SANITY_CHECKS */
 
+
 #if H5C_DO_SANITY_CHECKS
 
 #define H5C__INSERT_ENTRY_IN_SLIST(cache_ptr, entry_ptr, fail_val)             \
 {                                                                              \
     HDassert( (cache_ptr) );                                                   \
     HDassert( (cache_ptr)->magic == H5C__H5C_T_MAGIC );                        \
-    HDassert( (entry_ptr) );                                                   \
-    HDassert( (entry_ptr)->size > 0 );                                         \
-    HDassert( H5F_addr_defined((entry_ptr)->addr) );                           \
-    HDassert( !((entry_ptr)->in_slist) );                                      \
-    HDassert( !ENTRY_IN_SLIST((cache_ptr), (entry_ptr)) );                     \
-    HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                        \
-    HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                           \
-    HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=                \
-              (cache_ptr)->slist_len );                                        \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=               \
-              (cache_ptr)->slist_size );                                       \
                                                                                \
-    if(H5SL_insert((cache_ptr)->slist_ptr, entry_ptr, &(entry_ptr)->addr) < 0) \
-        HGOTO_ERROR(H5E_CACHE, H5E_BADVALUE, (fail_val), "can't insert entry in skip list") \
+    if ( (cache_ptr)->slist_enabled ) {                                        \
+                                                                               \
+        HDassert( (entry_ptr) );                                               \
+        HDassert( (entry_ptr)->size > 0 );                                     \
+        HDassert( H5F_addr_defined((entry_ptr)->addr) );                       \
+        HDassert( !((entry_ptr)->in_slist) );                                  \
+        HDassert( ! ENTRY_IN_SLIST((cache_ptr), (entry_ptr)) );                \
+        HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                    \
+        HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                       \
+        HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=            \
+                  (cache_ptr)->slist_len );                                    \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=           \
+                  (cache_ptr)->slist_size );                                   \
+                                                                               \
+        if ( H5SL_insert((cache_ptr)->slist_ptr, entry_ptr,                    \
+                         &((entry_ptr)->addr)) < 0)                            \
+            HGOTO_ERROR(H5E_CACHE, H5E_BADVALUE, (fail_val),                   \
+                        "can't insert entry in skip list")                     \
+                                                                               \
+        (entry_ptr)->in_slist = TRUE;                                          \
+        (cache_ptr)->slist_changed = TRUE;                                     \
+        (cache_ptr)->slist_len++;                                              \
+        (cache_ptr)->slist_size += (entry_ptr)->size;                          \
+        ((cache_ptr)->slist_ring_len[(entry_ptr)->ring])++;                    \
+        ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) += (entry_ptr)->size;\
+        (cache_ptr)->slist_len_increase++;                                     \
+        (cache_ptr)->slist_size_increase += (int64_t)((entry_ptr)->size);      \
                                                                                \
-    (entry_ptr)->in_slist = TRUE;                                              \
-    (cache_ptr)->slist_changed = TRUE;                                         \
-    (cache_ptr)->slist_len++;                                                  \
-    (cache_ptr)->slist_size += (entry_ptr)->size;                              \
-    ((cache_ptr)->slist_ring_len[(entry_ptr)->ring])++;                        \
-    ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) += (entry_ptr)->size;    \
-    (cache_ptr)->slist_len_increase++;                                         \
-    (cache_ptr)->slist_size_increase += (int64_t)((entry_ptr)->size);          \
+        HDassert( (cache_ptr)->slist_len > 0 );                                \
+        HDassert( (cache_ptr)->slist_size > 0 );                               \
                                                                                \
-    HDassert( (cache_ptr)->slist_len > 0 );                                    \
-    HDassert( (cache_ptr)->slist_size > 0 );                                   \
+    } else { /* slist disabled */                                              \
                                                                                \
+        HDassert( (cache_ptr)->slist_len == 0 );                               \
+        HDassert( (cache_ptr)->slist_size == 0 );                              \
+    }                                                                          \
 } /* H5C__INSERT_ENTRY_IN_SLIST */
 
 #else /* H5C_DO_SANITY_CHECKS */
@@ -1619,31 +1661,42 @@ if ( ( (cache_ptr)->index_size !=                                           \
 {                                                                              \
     HDassert( (cache_ptr) );                                                   \
     HDassert( (cache_ptr)->magic == H5C__H5C_T_MAGIC );                        \
-    HDassert( (entry_ptr) );                                                   \
-    HDassert( (entry_ptr)->size > 0 );                                         \
-    HDassert( H5F_addr_defined((entry_ptr)->addr) );                           \
-    HDassert( !((entry_ptr)->in_slist) );                                      \
-    HDassert( !ENTRY_IN_SLIST((cache_ptr), (entry_ptr)) );                     \
-    HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                        \
-    HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                           \
-    HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=                \
-              (cache_ptr)->slist_len );                                        \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=               \
-              (cache_ptr)->slist_size );                                       \
                                                                                \
-    if(H5SL_insert((cache_ptr)->slist_ptr, entry_ptr, &(entry_ptr)->addr) < 0) \
-        HGOTO_ERROR(H5E_CACHE, H5E_BADVALUE, (fail_val), "can't insert entry in skip list") \
+    if ( (cache_ptr)->slist_enabled ) {                                        \
+                                                                               \
+        HDassert( (entry_ptr) );                                               \
+        HDassert( (entry_ptr)->size > 0 );                                     \
+        HDassert( ! ENTRY_IN_SLIST((cache_ptr), (entry_ptr)) );                \
+        HDassert( H5F_addr_defined((entry_ptr)->addr) );                       \
+        HDassert( !((entry_ptr)->in_slist) );                                  \
+        HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                    \
+        HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                       \
+        HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=            \
+                  (cache_ptr)->slist_len );                                    \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=           \
+                  (cache_ptr)->slist_size );                                   \
+        HDassert( (cache_ptr)->slist_ptr );                                    \
+                                                                               \
+        if ( H5SL_insert((cache_ptr)->slist_ptr, entry_ptr,                    \
+                         &((entry_ptr)->addr)) < 0)                            \
+            HGOTO_ERROR(H5E_CACHE, H5E_BADVALUE, (fail_val),                   \
+                        "can't insert entry in skip list")                     \
                                                                                \
-    (entry_ptr)->in_slist = TRUE;                                              \
-    (cache_ptr)->slist_changed = TRUE;                                         \
-    (cache_ptr)->slist_len++;                                                  \
-    (cache_ptr)->slist_size += (entry_ptr)->size;                              \
-    ((cache_ptr)->slist_ring_len[(entry_ptr)->ring])++;                        \
-    ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) += (entry_ptr)->size;    \
+        (entry_ptr)->in_slist = TRUE;                                          \
+        (cache_ptr)->slist_changed = TRUE;                                     \
+        (cache_ptr)->slist_len++;                                              \
+        (cache_ptr)->slist_size += (entry_ptr)->size;                          \
+        ((cache_ptr)->slist_ring_len[(entry_ptr)->ring])++;                    \
+        ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) += (entry_ptr)->size;\
                                                                                \
-    HDassert( (cache_ptr)->slist_len > 0 );                                    \
-    HDassert( (cache_ptr)->slist_size > 0 );                                   \
+        HDassert( (cache_ptr)->slist_len > 0 );                                \
+        HDassert( (cache_ptr)->slist_size > 0 );                               \
                                                                                \
+    } else { /* slist disabled */                                              \
+                                                                               \
+        HDassert( (cache_ptr)->slist_len == 0 );                               \
+        HDassert( (cache_ptr)->slist_size == 0 );                              \
+    }                                                                          \
 } /* H5C__INSERT_ENTRY_IN_SLIST */
 
 #endif /* H5C_DO_SANITY_CHECKS */
@@ -1654,87 +1707,136 @@ if ( ( (cache_ptr)->index_size !=                                           \
  * Function:    H5C__REMOVE_ENTRY_FROM_SLIST
  *
  * Purpose:     Remove the specified instance of H5C_cache_entry_t from the
- *		index skip list in the specified instance of H5C_t.  Update
- *		the associated length and size fields.
+ *              index skip list in the specified instance of H5C_t.  Update
+ *              the associated length and size fields.
  *
  * Return:      N/A
  *
  * Programmer:  John Mainzer, 5/10/04
  *
+ * Modifications:
+ *
+ *              JRM -- 7/21/04
+ *              Updated function for the addition of the hash table.
+ *
+ *              JRM - 7/27/04
+ *              Converted from the function H5C_remove_entry_from_tree()
+ *              to the macro H5C__REMOVE_ENTRY_FROM_TREE in the hopes of
+ *              wringing a little more performance out of the cache.
+ *
+ *              QAK -- 11/27/04
+ *              Switched over to using skip list routines.
+ *
+ *              JRM -- 3/28/07
+ *              Updated sanity checks for the new is_read_only and
+ *              ro_ref_count fields in H5C_cache_entry_t.
+ *
+ *              JRM -- 12/13/14
+ *              Added code to set cache_ptr->slist_changed to TRUE
+ *              when an entry is removed from the slist.
+ *
+ *              JRM -- 4/29/20
+ *              Reworked macro to support the slist_enabled field 
+ *              of H5C_t.  If slist_enabled == TRUE, the macro 
+ *              functions as before.  Otherwise, the macro is a no-op,
+ *              and the slist must be empty.
+ *
  *-------------------------------------------------------------------------
  */
 
 #if H5C_DO_SANITY_CHECKS
-#define H5C__REMOVE_ENTRY_FROM_SLIST(cache_ptr, entry_ptr, during_flush)    \
-{                                                                           \
-    HDassert( (cache_ptr) );                                                \
-    HDassert( (cache_ptr)->magic == H5C__H5C_T_MAGIC );                     \
-    HDassert( (entry_ptr) );                                                \
-    HDassert( !((entry_ptr)->is_read_only) );                               \
-    HDassert( ((entry_ptr)->ro_ref_count) == 0 );                           \
-    HDassert( (entry_ptr)->size > 0 );                                      \
-    HDassert( (entry_ptr)->in_slist );                                      \
-    HDassert( (cache_ptr)->slist_ptr );                                     \
-    HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                     \
-    HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                        \
-    HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=             \
-              (cache_ptr)->slist_len );                                     \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=            \
-              (cache_ptr)->slist_size );                                    \
-                                                                            \
-    if ( H5SL_remove((cache_ptr)->slist_ptr, &(entry_ptr)->addr)            \
-             != (entry_ptr) )                                               \
-        HGOTO_ERROR(H5E_CACHE, H5E_BADVALUE, FAIL, "can't delete entry from skip list") \
-                                                                            \
-    HDassert( (cache_ptr)->slist_len > 0 );                                 \
-    if(!(during_flush))                                                     \
-        (cache_ptr)->slist_changed = TRUE;                                  \
-    (cache_ptr)->slist_len--;                                               \
-    HDassert( (cache_ptr)->slist_size >= (entry_ptr)->size );               \
-    (cache_ptr)->slist_size -= (entry_ptr)->size;                           \
-    ((cache_ptr)->slist_ring_len[(entry_ptr)->ring])--;                     \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr->ring)] >=            \
-              (entry_ptr)->size );                                          \
-    ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) -= (entry_ptr)->size; \
-    (cache_ptr)->slist_len_increase--;                                      \
-    (cache_ptr)->slist_size_increase -= (int64_t)((entry_ptr)->size);       \
-    (entry_ptr)->in_slist = FALSE;                                          \
+#define H5C__REMOVE_ENTRY_FROM_SLIST(cache_ptr, entry_ptr, during_flush)       \
+{                                                                              \
+    HDassert( (cache_ptr) );                                                   \
+    HDassert( (cache_ptr)->magic == H5C__H5C_T_MAGIC );                        \
+                                                                               \
+    if ( (cache_ptr)->slist_enabled ) {                                        \
+                                                                               \
+        HDassert( (entry_ptr) );                                               \
+        HDassert( !((entry_ptr)->is_read_only) );                              \
+        HDassert( ((entry_ptr)->ro_ref_count) == 0 );                          \
+        HDassert( (entry_ptr)->size > 0 );                                     \
+        HDassert( (entry_ptr)->in_slist );                                     \
+        HDassert( (cache_ptr)->slist_ptr );                                    \
+        HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                    \
+        HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                       \
+        HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=            \
+                  (cache_ptr)->slist_len );                                    \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=           \
+                  (cache_ptr)->slist_size );                                   \
+        HDassert( (cache_ptr)->slist_size >= (entry_ptr)->size );              \
+                                                                               \
+        if ( H5SL_remove((cache_ptr)->slist_ptr, &(entry_ptr)->addr)           \
+                 != (entry_ptr) )                                              \
+            HGOTO_ERROR(H5E_CACHE, H5E_BADVALUE, FAIL,                         \
+                        "can't delete entry from skip list")                   \
+                                                                               \
+        HDassert( (cache_ptr)->slist_len > 0 );                                \
+        if(!(during_flush))                                                    \
+            (cache_ptr)->slist_changed = TRUE;                                 \
+        (cache_ptr)->slist_len--;                                              \
+        HDassert( (cache_ptr)->slist_size >= (entry_ptr)->size );              \
+        (cache_ptr)->slist_size -= (entry_ptr)->size;                          \
+        ((cache_ptr)->slist_ring_len[(entry_ptr)->ring])--;                    \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr->ring)] >=           \
+                  (entry_ptr)->size );                                         \
+        ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) -= (entry_ptr)->size;\
+        (cache_ptr)->slist_len_increase--;                                     \
+        (cache_ptr)->slist_size_increase -= (int64_t)((entry_ptr)->size);      \
+        (entry_ptr)->in_slist = FALSE;                                         \
+                                                                               \
+    } else { /* slist disabled */                                              \
+                                                                               \
+        HDassert( (cache_ptr)->slist_len == 0 );                               \
+        HDassert( (cache_ptr)->slist_size == 0 );                               \
+    }                                                                          \
 } /* H5C__REMOVE_ENTRY_FROM_SLIST */
 
 #else /* H5C_DO_SANITY_CHECKS */
 
-#define H5C__REMOVE_ENTRY_FROM_SLIST(cache_ptr, entry_ptr, during_flush)    \
-{                                                                           \
-    HDassert( (cache_ptr) );                                                \
-    HDassert( (cache_ptr)->magic == H5C__H5C_T_MAGIC );                     \
-    HDassert( (entry_ptr) );                                                \
-    HDassert( !((entry_ptr)->is_read_only) );                               \
-    HDassert( ((entry_ptr)->ro_ref_count) == 0 );                           \
-    HDassert( (entry_ptr)->in_slist );                                      \
-    HDassert( (cache_ptr)->slist_ptr );                                     \
-    HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                     \
-    HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                        \
-    HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=             \
-              (cache_ptr)->slist_len );                                     \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=            \
-              (cache_ptr)->slist_size );                                    \
-                                                                            \
-    if ( H5SL_remove((cache_ptr)->slist_ptr, &(entry_ptr)->addr)            \
-             != (entry_ptr) )                                               \
-        HGOTO_ERROR(H5E_CACHE, H5E_BADVALUE, FAIL, "can't delete entry from skip list") \
-                                                                            \
-    HDassert( (cache_ptr)->slist_len > 0 );                                 \
-    if(!(during_flush))                                                     \
-        (cache_ptr)->slist_changed = TRUE;                                  \
-    (cache_ptr)->slist_len--;                                               \
-    HDassert( (cache_ptr)->slist_size >= (entry_ptr)->size );               \
-    (cache_ptr)->slist_size -= (entry_ptr)->size;                           \
-    ((cache_ptr)->slist_ring_len[(entry_ptr)->ring])--;                     \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr->ring)] >=            \
-              (entry_ptr)->size );                                          \
-    ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) -= (entry_ptr)->size; \
-    (entry_ptr)->in_slist = FALSE;                                          \
+#define H5C__REMOVE_ENTRY_FROM_SLIST(cache_ptr, entry_ptr, during_flush)       \
+{                                                                              \
+    HDassert( (cache_ptr) );                                                   \
+    HDassert( (cache_ptr)->magic == H5C__H5C_T_MAGIC );                        \
+                                                                               \
+    if ( (cache_ptr)->slist_enabled ) {                                        \
+                                                                               \
+        HDassert( (entry_ptr) );                                               \
+        HDassert( !((entry_ptr)->is_read_only) );                              \
+        HDassert( ((entry_ptr)->ro_ref_count) == 0 );                          \
+        HDassert( (entry_ptr)->in_slist );                                     \
+        HDassert( (cache_ptr)->slist_ptr );                                    \
+        HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                    \
+        HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                       \
+        HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=            \
+                  (cache_ptr)->slist_len );                                    \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=           \
+                  (cache_ptr)->slist_size );                                   \
+                                                                               \
+        if ( H5SL_remove((cache_ptr)->slist_ptr, &(entry_ptr)->addr)           \
+             != (entry_ptr) )                                                  \
+            HGOTO_ERROR(H5E_CACHE, H5E_BADVALUE, FAIL,                         \
+                        "can't delete entry from skip list")                   \
+                                                                               \
+        HDassert( (cache_ptr)->slist_len > 0 );                                \
+        if(!(during_flush))                                                    \
+            (cache_ptr)->slist_changed = TRUE;                                 \
+        (cache_ptr)->slist_len--;                                              \
+        HDassert( (cache_ptr)->slist_size >= (entry_ptr)->size );              \
+        (cache_ptr)->slist_size -= (entry_ptr)->size;                          \
+        ((cache_ptr)->slist_ring_len[(entry_ptr)->ring])--;                    \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr->ring)] >=           \
+                  (entry_ptr)->size );                                         \
+        ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) -= (entry_ptr)->size;\
+        (entry_ptr)->in_slist = FALSE;                                         \
+                                                                               \
+    } else { /* slist disabled */                                              \
+                                                                               \
+        HDassert( (cache_ptr)->slist_len == 0 );                               \
+        HDassert( (cache_ptr)->slist_size == 0 );                              \
+    }                                                                          \
 } /* H5C__REMOVE_ENTRY_FROM_SLIST */
+
 #endif /* H5C_DO_SANITY_CHECKS */
 
 
@@ -1743,7 +1845,7 @@ if ( ( (cache_ptr)->index_size !=                                           \
  * Function:    H5C__UPDATE_SLIST_FOR_SIZE_CHANGE
  *
  * Purpose:     Update cache_ptr->slist_size for a change in the size of
- *		and entry in the slist.
+ *              and entry in the slist.
  *
  * Return:      N/A
  *
@@ -1751,24 +1853,30 @@ if ( ( (cache_ptr)->index_size !=                                           \
  *
  * Modifications:
  *
- *		JRM -- 8/27/06
- *		Added the H5C_DO_SANITY_CHECKS version of the macro.
+ *              JRM -- 8/27/06
+ *              Added the H5C_DO_SANITY_CHECKS version of the macro.
  *
- *		This version maintains the slist_size_increase field
- *		that are used in sanity checks in the flush routines.
+ *              This version maintains the slist_size_increase field
+ *              that are used in sanity checks in the flush routines.
  *
- *		All this is needed as the fractal heap needs to be
- *		able to dirty, resize and/or move entries during the
- *		flush.
+ *              All this is needed as the fractal heap needs to be
+ *              able to dirty, resize and/or move entries during the
+ *              flush.
  *
- *		JRM -- 12/13/14
- *		Note that we do not set cache_ptr->slist_changed to TRUE
- *		in this case, as the structure of the slist is not
- *		modified.
+ *              JRM -- 12/13/14
+ *              Note that we do not set cache_ptr->slist_changed to TRUE
+ *              in this case, as the structure of the slist is not
+ *              modified.
  *
- *		JRM -- 9/1/15
- *		Added code to maintain the cache_ptr->slist_ring_len
- *		and cache_ptr->slist_ring_size arrays.
+ *              JRM -- 9/1/15
+ *              Added code to maintain the cache_ptr->slist_ring_len
+ *              and cache_ptr->slist_ring_size arrays.
+ *
+ *              JRM -- 4/29/20
+ *              Reworked macro to support the slist_enabled field 
+ *              of H5C_t.  If slist_enabled == TRUE, the macro 
+ *              functions as before.  Otherwise, the macro is a no-op,
+ *              and the slist must be empty.
  *
  *-------------------------------------------------------------------------
  */
@@ -1779,32 +1887,43 @@ if ( ( (cache_ptr)->index_size !=                                           \
 {                                                                             \
     HDassert( (cache_ptr) );                                                  \
     HDassert( (cache_ptr)->magic == H5C__H5C_T_MAGIC );                       \
-    HDassert( (old_size) > 0 );                                               \
-    HDassert( (new_size) > 0 );                                               \
-    HDassert( (old_size) <= (cache_ptr)->slist_size );                        \
-    HDassert( (cache_ptr)->slist_len > 0 );                                   \
-    HDassert( ((cache_ptr)->slist_len > 1) ||                                 \
-              ( (cache_ptr)->slist_size == (old_size) ) );                    \
-    HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                       \
-    HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                          \
-    HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=               \
-              (cache_ptr)->slist_len );                                       \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=              \
-              (cache_ptr)->slist_size );                                      \
                                                                               \
-    (cache_ptr)->slist_size -= (old_size);                                    \
-    (cache_ptr)->slist_size += (new_size);                                    \
+    if ( (cache_ptr)->slist_enabled ) {                                       \
+                                                                              \
+        HDassert( (old_size) > 0 );                                           \
+        HDassert( (new_size) > 0 );                                           \
+        HDassert( (old_size) <= (cache_ptr)->slist_size );                    \
+        HDassert( (cache_ptr)->slist_len > 0 );                               \
+        HDassert( ((cache_ptr)->slist_len > 1) ||                             \
+                  ( (cache_ptr)->slist_size == (old_size) ) );                \
+        HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                   \
+        HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                      \
+        HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=           \
+                  (cache_ptr)->slist_len );                                   \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=          \
+                  (cache_ptr)->slist_size );                                  \
+                                                                              \
+        (cache_ptr)->slist_size -= (old_size);                                \
+        (cache_ptr)->slist_size += (new_size);                                \
                                                                               \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr->ring)] >=(old_size) ); \
-    ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) -= (old_size);          \
-    ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) += (new_size);          \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr->ring)]             \
+                  >= (old_size) );                                            \
                                                                               \
-    (cache_ptr)->slist_size_increase -= (int64_t)(old_size);                  \
-    (cache_ptr)->slist_size_increase += (int64_t)(new_size);                  \
+        ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) -= (old_size);      \
+        ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) += (new_size);      \
                                                                               \
-    HDassert( (new_size) <= (cache_ptr)->slist_size );                        \
-    HDassert( ( (cache_ptr)->slist_len > 1 ) ||                               \
-              ( (cache_ptr)->slist_size == (new_size) ) );                    \
+        (cache_ptr)->slist_size_increase -= (int64_t)(old_size);              \
+        (cache_ptr)->slist_size_increase += (int64_t)(new_size);              \
+                                                                              \
+        HDassert( (new_size) <= (cache_ptr)->slist_size );                    \
+        HDassert( ( (cache_ptr)->slist_len > 1 ) ||                           \
+                  ( (cache_ptr)->slist_size == (new_size) ) );                \
+                                                                              \
+    } else { /* slist disabled */                                             \
+                                                                              \
+        HDassert( (cache_ptr)->slist_len == 0 );                              \
+        HDassert( (cache_ptr)->slist_size == 0 );                             \
+    }                                                                         \
 } /* H5C__UPDATE_SLIST_FOR_SIZE_CHANGE */
 
 #else /* H5C_DO_SANITY_CHECKS */
@@ -1813,29 +1932,39 @@ if ( ( (cache_ptr)->index_size !=                                           \
 {                                                                             \
     HDassert( (cache_ptr) );                                                  \
     HDassert( (cache_ptr)->magic == H5C__H5C_T_MAGIC );                       \
-    HDassert( (old_size) > 0 );                                               \
-    HDassert( (new_size) > 0 );                                               \
-    HDassert( (old_size) <= (cache_ptr)->slist_size );                        \
-    HDassert( (cache_ptr)->slist_len > 0 );                                   \
-    HDassert( ((cache_ptr)->slist_len > 1) ||                                 \
-              ( (cache_ptr)->slist_size == (old_size) ) );                    \
-    HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                       \
-    HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                          \
-    HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=               \
-              (cache_ptr)->slist_len );                                       \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=              \
-              (cache_ptr)->slist_size );                                      \
                                                                               \
-    (cache_ptr)->slist_size -= (old_size);                                    \
-    (cache_ptr)->slist_size += (new_size);                                    \
+    if ( (cache_ptr)->slist_enabled ) {                                       \
+                                                                              \
+        HDassert( (old_size) > 0 );                                           \
+        HDassert( (new_size) > 0 );                                           \
+        HDassert( (old_size) <= (cache_ptr)->slist_size );                    \
+        HDassert( (cache_ptr)->slist_len > 0 );                               \
+        HDassert( ((cache_ptr)->slist_len > 1) ||                             \
+                  ( (cache_ptr)->slist_size == (old_size) ) );                \
+        HDassert( (entry_ptr)->ring > H5C_RING_UNDEFINED );                   \
+        HDassert( (entry_ptr)->ring < H5C_RING_NTYPES );                      \
+        HDassert( (cache_ptr)->slist_ring_len[(entry_ptr)->ring] <=           \
+                  (cache_ptr)->slist_len );                                   \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr)->ring] <=          \
+                  (cache_ptr)->slist_size );                                  \
+                                                                              \
+        (cache_ptr)->slist_size -= (old_size);                                \
+        (cache_ptr)->slist_size += (new_size);                                \
                                                                               \
-    HDassert( (cache_ptr)->slist_ring_size[(entry_ptr->ring)] >=(old_size) ); \
-    ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) -= (old_size);          \
-    ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) += (new_size);          \
+        HDassert( (cache_ptr)->slist_ring_size[(entry_ptr->ring)] >=          \
+                  (old_size) );                                               \
+        ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) -= (old_size);      \
+        ((cache_ptr)->slist_ring_size[(entry_ptr)->ring]) += (new_size);      \
                                                                               \
-    HDassert( (new_size) <= (cache_ptr)->slist_size );                        \
-    HDassert( ( (cache_ptr)->slist_len > 1 ) ||                               \
-              ( (cache_ptr)->slist_size == (new_size) ) );                    \
+        HDassert( (new_size) <= (cache_ptr)->slist_size );                    \
+        HDassert( ( (cache_ptr)->slist_len > 1 ) ||                           \
+                  ( (cache_ptr)->slist_size == (new_size) ) );                \
+                                                                              \
+    } else { /* slist disabled */                                             \
+                                                                              \
+        HDassert( (cache_ptr)->slist_len == 0 );                              \
+        HDassert( (cache_ptr)->slist_size == 0 );                             \
+    }                                                                         \
 } /* H5C__UPDATE_SLIST_FOR_SIZE_CHANGE */
 
 #endif /* H5C_DO_SANITY_CHECKS */
@@ -3723,10 +3852,11 @@ typedef struct H5C_tag_info_t {
  *		one.
  *
  * entry_watched_for_removal:	Pointer to an instance of H5C_cache_entry_t
- *		which contains the 'next' entry for an iteration.  Removing
+ *              which contains the 'next' entry for an iteration.  Removing
  *              this entry must trigger a rescan of the iteration, so each
  *              entry removed from the cache is compared against this pointer
- *              and the pointer is reset to NULL if the watched entry is removed.
+ *              and the pointer is reset to NULL if the watched entry is 
+ *              removed.
  *              (This functions similarly to a "dead man's switch")
  *
  *
@@ -3740,6 +3870,36 @@ typedef struct H5C_tag_info_t {
  * are flushed. (this has been changed -- dirty entries are now removed from
  * the skip list as they are flushed.  JRM - 10/25/05)
  *
+ * Update 4/21/20: 
+ *
+ * Profiling indicates that the cost of maintaining the skip list is 
+ * significant.  As it is only used on flush and close, maintaining it
+ * only when needed is an obvious optimization.
+ *
+ * To do this, we add a flag to control maintenanace of the skip list.
+ * This flag is initially set to FALSE, which disables all operations 
+ * on the skip list.
+ *
+ * At the beginning of either flush or close, we scan the index list,
+ * insert all dirtly entries in the skip list, and enable operations
+ * on skip list by setting above control flag to true.
+ *
+ * At the end of a complete flush, we verify that the skip list is empty,
+ * and set the control flag back to false, so as to avoid skip list 
+ * maintenance overhead until the next flush or close.  
+ *
+ * In the case of a partial flush (i.e. flush marked entries), we remove
+ * all remaining entries from the skip list, and then set the control flag
+ * back to false -- again avoiding skip list maintenance overhead until 
+ * the next flush or close.
+ *
+ * slist_enabled: Boolean flag used to control operation of the skip
+ *              list.  If this filed is FALSE, operations on the 
+ *              slist are no-ops, and the slist must be empty.  If
+ *              it is TRUE, operations on the slist proceed as usual,
+ *              and all dirty entries in the metadata cache must be
+ *              listed in the slist.
+ *
  * slist_changed: Boolean flag used to indicate whether the contents of
  *		the slist has changed since the last time this flag was
  *		reset.  This is used in the cache flush code to detect
@@ -4649,6 +4809,7 @@ typedef struct H5C_tag_info_t {
  *              NDEBUG is not #defined.
  *
  ****************************************************************************/
+
 struct H5C_t {
     uint32_t			magic;
     hbool_t			flush_in_progress;
@@ -4664,7 +4825,7 @@ struct H5C_t {
     hbool_t			evictions_enabled;
     hbool_t			close_warning_received;
 
-    /* Fields for maintaining [hash table] index of entries */
+    /* Fields for maintaining the [hash table] index of entries */
     uint32_t                    index_len;
     size_t                      index_size;
     uint32_t			index_ring_len[H5C_RING_NTYPES];
@@ -4685,6 +4846,7 @@ struct H5C_t {
     H5C_cache_entry_t *		entry_watched_for_removal;
 
     /* Fields for maintaining list of in-order entries, for flushing */
+    hbool_t                     slist_enabled;
     hbool_t			slist_changed;
     uint32_t                    slist_len;
     size_t                      slist_size;
@@ -4882,7 +5044,8 @@ struct H5C_t {
 #ifndef NDEBUG
     int64_t                     get_entry_ptr_from_addr_counter;
 #endif /* NDEBUG */
-};
+
+}; /* H5C_t */
 
 /* Define typedef for tagged cache entry iteration callbacks */
 typedef int (*H5C_tag_iter_cb_t)(H5C_cache_entry_t *entry, void *ctx);
diff --git a/src/H5Cprivate.h b/src/H5Cprivate.h
index 7f79452..3203da6 100644
--- a/src/H5Cprivate.h
+++ b/src/H5Cprivate.h
@@ -2287,7 +2287,10 @@ H5_DLL herr_t H5C_resize_entry(void *thing, size_t new_size);
 H5_DLL herr_t H5C_set_cache_auto_resize_config(H5C_t *cache_ptr, H5C_auto_size_ctl_t *config_ptr);
 H5_DLL herr_t H5C_set_cache_image_config(const H5F_t *f, H5C_t *cache_ptr,
     H5C_cache_image_ctl_t *config_ptr);
-H5_DLL herr_t H5C_set_evictions_enabled(H5C_t *cache_ptr, hbool_t evictions_enabled);
+H5_DLL herr_t H5C_set_evictions_enabled(H5C_t *cache_ptr, 
+    hbool_t evictions_enabled);
+H5_DLL herr_t H5C_set_slist_enabled(H5C_t *cache_ptr, hbool_t slist_enabled,
+    hbool_t clear_slist);
 H5_DLL herr_t H5C_set_prefix(H5C_t *cache_ptr, char *prefix);
 H5_DLL herr_t H5C_stats(H5C_t *cache_ptr, const char *cache_name,
     hbool_t display_detailed_stats);
diff --git a/src/H5Fint.c b/src/H5Fint.c
index 29bbd45..9dad1d7 100644
--- a/src/H5Fint.c
+++ b/src/H5Fint.c
@@ -1971,6 +1971,11 @@ H5F__flush_phase2(H5F_t *f, hbool_t closing)
     /* Sanity check arguments */
     HDassert(f);
 
+    /* Inform the metadata cache that we are about to flush */
+    if(H5AC_prep_for_file_flush(f) < 0)
+        /* Push error, but keep going*/
+        HDONE_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "prep for MDC flush failed")
+
     /* Flush the entire metadata cache */
     if(H5AC_flush(f) < 0)
         /* Push error, but keep going*/
@@ -2003,6 +2008,11 @@ H5F__flush_phase2(H5F_t *f, hbool_t closing)
         H5CX_set_mpi_file_flushing(FALSE);
 #endif /* H5_HAVE_PARALLEL */
 
+    /* Inform the metadata cache that we are done with the flush */
+    if(H5AC_secure_from_file_flush(f) < 0)
+        /* Push error, but keep going*/
+        HDONE_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "secure from MDC flush failed")
+
     /* Flush out the metadata accumulator */
     if(H5F__accum_flush(f->shared) < 0)
         /* Push error, but keep going*/