path: root/src/H5PB.c

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * Copyright by the Board of Trustees of the University of Illinois.         *
 * All rights reserved.                                                      *
 *                                                                           *
 * This file is part of HDF5.  The full HDF5 copyright notice, including     *
 * terms governing use, modification, and redistribution, is contained in    *
 * the COPYING file, which can be found at the root of the source code       *
 * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
 * If you do not have access to either file, you may request a copy from     *
 * help@hdfgroup.org.                                                        *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/*-------------------------------------------------------------------------
 *
 * Created:  H5PB2.c
 * 
 * Purpose:  Re-implementation of the page buffer with added features to 
 *           support VFD SWMR.
 *                                              JRM -- 10/11/18
 *
 *-------------------------------------------------------------------------
 */

/****************/
/* Module Setup */
/****************/

#define H5F_FRIEND		/* suppress error about including H5Fpkg */
#include "H5PBmodule.h"         /* This source code file is part of the 
                                 * H5PB module 
                                 */


/***********/
/* Headers */
/***********/
#include "H5private.h"		/* Generic Functions			*/
#include "H5Eprivate.h"		/* Error handling		  	*/
#include "H5Fpkg.h"		/* Files				*/
#include "H5FDprivate.h"	/* File drivers				*/
#include "H5Iprivate.h"		/* IDs			  		*/
#include "H5FLprivate.h"        /* Free lists                           */
#include "H5MMprivate.h"        /* Memory management                    */
#include "H5PBpkg.h"            /* File access				*/


/****************/
/* Local Macros */
/****************/

/* In principle, we should be able to run the page buffer with the 
 * accumulator.  However, for whatever reason, the fheap test encounteres
 * metadata corruption if the page buffer uses H5F__accum_read/write()
 * for I/O.
 *
 * The following #define controls this.  Set VFD_IO to FALSE to reproduce
 * the bug.
 */
#define VFD_IO FALSE


/******************/
/* Local Typedefs */
/******************/


/********************/
/* Package Typedefs */
/********************/


/********************/
/* Local Prototypes */
/********************/

static H5PB_entry_t * H5PB__allocate_page(H5PB_t *pb_ptr, size_t buf_size, 
    hbool_t clean_image);

static herr_t H5PB__create_new_page(H5PB_t *pb_ptr, haddr_t addr, size_t size,
    H5FD_mem_t type, hbool_t clean_image, H5PB_entry_t **entry_ptr_ptr);

static void H5PB__deallocate_page(H5PB_entry_t *entry_ptr);

static herr_t H5PB__evict_entry(H5PB_t *pb_ptr, H5PB_entry_t *entry_ptr, 
    hbool_t force);

static herr_t H5PB__flush_entry(H5F_t *f, H5PB_t *pb_ptr, 
    H5PB_entry_t *entry_ptr);

static herr_t H5PB__load_page(H5F_t *f, H5PB_t *pb_ptr, haddr_t addr, 
    H5FD_mem_t type, H5PB_entry_t **entry_ptr_ptr);

static herr_t H5PB__make_space(H5F_t *f, H5PB_t *pb_ptr, 
    H5FD_mem_t inserted_type);

static herr_t H5PB__mark_entry_clean(H5PB_t *pb_ptr, 
    H5PB_entry_t *entry_ptr);

static herr_t H5PB__mark_entry_dirty(H5F_t * f, H5PB_t *pb_ptr, 
    H5PB_entry_t *entry_ptr);

static herr_t H5PB__read_meta(H5F_t *f, H5FD_mem_t type, haddr_t addr, 
    size_t size, void *buf/*out*/);

static herr_t H5PB__read_raw(H5F_t *f, H5FD_mem_t type, haddr_t addr, 
    size_t size, void *buf/*out*/);

static herr_t H5PB__write_meta(H5F_t *f, H5FD_mem_t type, haddr_t addr, 
    size_t size, const void *buf/*out*/);

static herr_t H5PB__write_raw(H5F_t *f, H5FD_mem_t type, haddr_t addr, 
    size_t size, const void *buf/*out*/);


/*********************/
/* Package Variables */
/*********************/

/* Package initialization variable */
hbool_t H5_PKG_INIT_VAR = FALSE;


/*****************************/
/* Library Private Variables */
/*****************************/


/*******************/
/* Local Variables */
/*******************/


/* Declare a free list to manage the H5PB_t struct */
H5FL_DEFINE_STATIC(H5PB_t);

/* Declare a free list to manage the H5PB_entry_t struct */
H5FL_DEFINE_STATIC(H5PB_entry_t);



/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_reset_stats
 *
 * Purpose:     Reset statistics collected for the page buffer layer.
 *
 * Return:      Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/12/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t 
H5PB_reset_stats(H5PB_t *pb_ptr)
{
    int i;

    FUNC_ENTER_NOAPI_NOERR

    /* Sanity checks */
    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);

    for ( i = 0; i < H5PB__NUM_STAT_TYPES; i++ ) {

        pb_ptr->bypasses[i]   = 0;
        pb_ptr->accesses[i]   = 0;
        pb_ptr->hits[i]       = 0;
        pb_ptr->misses[i]     = 0;
        pb_ptr->loads[i]      = 0;
        pb_ptr->insertions[i] = 0;
        pb_ptr->flushes[i]    = 0;
        pb_ptr->evictions[i]  = 0;
        pb_ptr->clears[i]     = 0;
    }
    
    pb_ptr->max_lru_len                      = 0;
    pb_ptr->max_lru_size                     = 0;
    pb_ptr->lru_md_skips                     = 0;
    pb_ptr->lru_rd_skips                     = 0;
    pb_ptr->total_ht_insertions              = 0;
    pb_ptr->total_ht_deletions               = 0;
    pb_ptr->successful_ht_searches           = 0;
    pb_ptr->total_successful_ht_search_depth = 0;
    pb_ptr->failed_ht_searches               = 0;
    pb_ptr->total_failed_ht_search_depth     = 0;
    pb_ptr->max_index_len                    = 0;
    pb_ptr->max_clean_index_len              = 0;
    pb_ptr->max_dirty_index_len              = 0;
    pb_ptr->max_clean_index_size             = 0;
    pb_ptr->max_dirty_index_size             = 0;
    pb_ptr->max_index_size                   = 0;
    pb_ptr->max_rd_pages                     = 0;
    pb_ptr->max_md_pages                     = 0;
    pb_ptr->max_mpmde_count                  = 0;
    pb_ptr->lru_tl_skips                     = 0;
    pb_ptr->max_tl_len                       = 0;
    pb_ptr->max_tl_size                      = 0;
    pb_ptr->delayed_writes                   = 0;
    pb_ptr->total_delay                      = 0;
    pb_ptr->max_dwl_len                      = 0;
    pb_ptr->max_dwl_size                     = 0;
    pb_ptr->total_dwl_ins_depth              = 0;

    FUNC_LEAVE_NOAPI(SUCCEED)

}  /* H5PB_reset_stats() */


/*-------------------------------------------------------------------------
 * Function:	H5PB_get_stats
 *
 * Purpose:     This function was created without documentation.
 *              What follows is my best understanding of Mohamad's intent.
 *
 *              Retrieve statistics collected about page accesses for the 
 *              page buffer layer.
 *
 *              --accesses: the number of metadata and raw data accesses 
 *                          to the page buffer layer
 *
 *              --hits: the number of metadata and raw data hits in 
 *                          the page buffer layer
 *
 *              --misses: the number of metadata and raw data misses in 
 *                          the page buffer layer
 *
 *              --evictions: the number of metadata and raw data evictions 
 *                          from the page buffer layer
 *
 *              --bypasses: the number of metadata and raw data accesses 
 *                          that bypass the page buffer layer
 *
 * Return:	    Non-negative on success/Negative on failure
 *
 * Programmer:	Mohamad Chaarawi
 *
 *-------------------------------------------------------------------------
 */
herr_t 
H5PB_get_stats(const H5PB_t *pb_ptr, unsigned accesses[2], unsigned hits[2],
    unsigned misses[2], unsigned evictions[2], unsigned bypasses[2])
{
    FUNC_ENTER_NOAPI_NOERR

    /* Sanity checks */
    HDassert(pb_ptr);

    accesses[0] = (unsigned)pb_ptr->accesses[0];
    accesses[1] = (unsigned)pb_ptr->accesses[1];
    accesses[2] = (unsigned)pb_ptr->accesses[2];
    hits[0] = (unsigned)pb_ptr->hits[0];
    hits[1] = (unsigned)pb_ptr->hits[1];
    hits[2] = (unsigned)pb_ptr->hits[2];
    misses[0] = (unsigned)pb_ptr->misses[0];
    misses[1] = (unsigned)pb_ptr->misses[1];
    misses[2] = (unsigned)pb_ptr->misses[2];
    evictions[0] = (unsigned)pb_ptr->evictions[0];
    evictions[1] = (unsigned)pb_ptr->evictions[1];
    evictions[2] = (unsigned)pb_ptr->evictions[2];
    bypasses[0] = (unsigned)pb_ptr->bypasses[0];
    bypasses[1] = (unsigned)pb_ptr->bypasses[1];
    bypasses[2] = (unsigned)pb_ptr->bypasses[2];

    FUNC_LEAVE_NOAPI(SUCCEED)
}  /* H5PB_get_stats */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_print_stats()
 *
 * Purpose:     Print out statistics collected for the page buffer layer.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/12/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5PB_print_stats(const H5PB_t *pb_ptr)
{
    double ave_succ_search_depth = 0.0L;
    double ave_failed_search_depth = 0.0L;
    double ave_delayed_write = 0.0L;
    double ave_delayed_write_ins_depth = 0.0L;

    FUNC_ENTER_NOAPI_NOINIT_NOERR

    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);

    HDfprintf(stdout, "\n\nPage Buffer Statistics (raw/meta/mpmde): \n\n");

    HDfprintf(stdout, "bypasses   = %lld (%lld/%lld/%lld)\n",
              (pb_ptr->bypasses[0] + pb_ptr->bypasses[1] + pb_ptr->bypasses[2]),
              pb_ptr->bypasses[0], pb_ptr->bypasses[1], pb_ptr->bypasses[2]);

    HDfprintf(stdout, "acesses    = %lld (%lld/%lld/%lld)\n",
              (pb_ptr->accesses[0] + pb_ptr->accesses[1] + pb_ptr->accesses[2]),
              pb_ptr->accesses[0], pb_ptr->accesses[1], pb_ptr->accesses[2]);

    HDfprintf(stdout, "hits       = %lld (%lld/%lld/%lld)\n",
              (pb_ptr->hits[0] + pb_ptr->hits[1] + pb_ptr->hits[2]),
              pb_ptr->hits[0], pb_ptr->hits[1], pb_ptr->hits[2]);

    HDfprintf(stdout, "misses     = %lld (%lld/%lld/%lld)\n",
              (pb_ptr->misses[0] + pb_ptr->misses[1] + pb_ptr->misses[2]),
              pb_ptr->misses[0], pb_ptr->misses[1], pb_ptr->misses[2]);

    HDfprintf(stdout, "loads      = %lld (%lld/%lld/%lld)\n",
              (pb_ptr->loads[0] + pb_ptr->loads[1] + pb_ptr->loads[2]),
              pb_ptr->loads[0], pb_ptr->loads[1], pb_ptr->loads[2]);

    HDfprintf(stdout, "insertions = %lld (%lld/%lld/%lld)\n",
              (pb_ptr->insertions[0] + pb_ptr->insertions[1] + 
               pb_ptr->insertions[2]),
              pb_ptr->insertions[0], pb_ptr->insertions[1], 
              pb_ptr->insertions[2]);

    HDfprintf(stdout, "flushes    = %lld (%lld/%lld/%lld)\n",
              (pb_ptr->flushes[0] + pb_ptr->flushes[1] + pb_ptr->flushes[2]),
              pb_ptr->flushes[0], pb_ptr->flushes[1], pb_ptr->flushes[2]);

    HDfprintf(stdout, "evictions  = %lld (%lld/%lld/%lld)\n",
              (pb_ptr->evictions[0] + pb_ptr->evictions[1] + 
               pb_ptr->evictions[2]),
              pb_ptr->evictions[0], pb_ptr->evictions[1], pb_ptr->evictions[2]);

    HDfprintf(stdout, "clears     = %lld (%lld/%lld/%lld)\n",
              (pb_ptr->clears[0] + pb_ptr->clears[1] + pb_ptr->clears[2]),
              pb_ptr->clears[0], pb_ptr->clears[1], pb_ptr->clears[2]);
              
    HDfprintf(stdout, "max LRU len / size = %lld / %lld\n",
              pb_ptr->max_lru_len, pb_ptr->max_lru_size);

    HDfprintf(stdout, 
              "LRU make space md/rd/tl skips = %lld/%lld/%lld\n",
              pb_ptr->lru_md_skips, pb_ptr->lru_rd_skips, 
              pb_ptr->lru_tl_skips);

    HDfprintf(stdout, "hash table insertions / deletions = %lld / %lld\n",
              pb_ptr->total_ht_insertions, pb_ptr->total_ht_deletions);

    if ( pb_ptr->successful_ht_searches > 0 ) {

        ave_succ_search_depth = 
            (double)(pb_ptr->total_successful_ht_search_depth) / 
            (double)(pb_ptr->successful_ht_searches);
    }
    HDfprintf(stdout, "successful ht searches / ave depth = %lld / %llf\n",
              pb_ptr->successful_ht_searches, ave_succ_search_depth);

    if ( pb_ptr->failed_ht_searches > 0 ) {

        ave_failed_search_depth = 
            (double)(pb_ptr->total_failed_ht_search_depth) / 
            (double)(pb_ptr->failed_ht_searches);
    }
    HDfprintf(stdout, "failed ht searches / ave depth = %lld / %llf\n",
              pb_ptr->failed_ht_searches, ave_failed_search_depth);

    HDfprintf(stdout, "max index length / size = %lld / %lld\n",
              pb_ptr->max_index_len, pb_ptr->max_index_size);

    HDfprintf(stdout, "max rd / md / mpmde entries = %lld / %lld / %lld\n",
              pb_ptr->max_rd_pages, pb_ptr->max_md_pages, 
              pb_ptr->max_mpmde_count);

    HDfprintf(stdout, "tick list max len / size = %lld / %lld\n",
              pb_ptr->max_tl_len, pb_ptr->max_tl_size);

    HDfprintf(stdout, "delayed write list max len / size = %lld / %lld\n",
              pb_ptr->max_dwl_len, pb_ptr->max_dwl_size);

    if ( pb_ptr->delayed_writes > 0 ) {

        ave_delayed_write = (double)(pb_ptr->total_delay) / 
                            (double)(pb_ptr->delayed_writes);
        ave_delayed_write_ins_depth = (double)(pb_ptr->total_dwl_ins_depth) /
                                      (double)(pb_ptr->delayed_writes);
    }
    HDfprintf(stdout, 
        "delayed writes / ave delay / ave ins depth = %lld / %llf / %llf\n",
        pb_ptr->delayed_writes, ave_delayed_write, ave_delayed_write_ins_depth);

    FUNC_LEAVE_NOAPI(SUCCEED)

} /* H5PB_print_stats */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_add_new_page
 *
 * Purpose:	Insert a new blank page to the page buffer if the page 
 *              buffer is configured to allow pages of the specified
 *              type.
 *
 *              This function is called by the MF layer when a new page 
 *              is allocated to indicate to the page buffer layer that 
 *              a read of the page from the file is not necessary since 
 *              it's an empty page.
 *
 *              For purposes of the VFD SWMR writer, we also track pages
 *              that are inserted via this call, as the fact that the 
 *              page was allocated implies that an earlier version does
 *              not exist in the HDF5 file, and thus we need not concern
 *              ourselves with delaying the write of this pages to avoid 
 *              messages from the future on the reader.
 *
 *              Note that this function inserts the new page without 
 *              attempting to make space.  This can result in the page 
 *              buffer exceeding its maximum size.
 *
 *              Note also that it is possible that the page (marked clean)
 *              will be evicted before its first use.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/12/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t 
H5PB_add_new_page(H5F_t *f, H5FD_mem_t type, haddr_t page_addr)
{
    hbool_t can_insert = TRUE;
    H5PB_t *pb_ptr = NULL;
    H5PB_entry_t *entry_ptr = NULL;
    herr_t ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->pb_ptr);

    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);

    if ( H5FD_MEM_DRAW == type ) { /* raw data page insertion */

        if ( pb_ptr->min_md_pages == pb_ptr->max_pages ) {

            can_insert = FALSE;

        }
    } else { /* metadata page insertion */

        if ( pb_ptr->min_rd_pages == pb_ptr->max_pages ) {

            can_insert = FALSE;
        }
    }

    if ( can_insert ) {

        if ( H5PB__create_new_page(pb_ptr, page_addr, 
                                   (size_t)(pb_ptr->page_size),
                                   type, TRUE, &entry_ptr) < 0 )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                        "new page buffer page creation failed.")

        /* make note that this page was allocated, not loaded from file */
        entry_ptr->loaded = FALSE;

        /* updates stats */
        H5PB__UPDATE_STATS_FOR_INSERTION(pb_ptr, entry_ptr);
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_add_new_page */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_create
 *
 * Purpose:	Setup a page buffer for the supplied file.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/11/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5PB_create(H5F_t *f, size_t size, unsigned page_buf_min_meta_perc, 
            unsigned page_buf_min_raw_perc)
{
    hbool_t vfd_swmr_writer = FALSE;
    int i;
    int32_t min_md_pages;
    int32_t min_rd_pages;
    H5PB_t *pb_ptr = NULL;
    herr_t ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(page_buf_min_meta_perc <= 100);
    HDassert(page_buf_min_raw_perc <= 100);
    HDassert((page_buf_min_meta_perc + page_buf_min_raw_perc) <= 100);

    /* Check args */
    if ( f->shared->fs_strategy != H5F_FSPACE_STRATEGY_PAGE )

        HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, \
                    "Enabling Page Buffering requires PAGE file space strategy")

    else if ( size > f->shared->fs_page_size ) {

        /* round size down to the next multiple of fs_page_size */

        hsize_t temp_size;

        temp_size = (size / f->shared->fs_page_size) * f->shared->fs_page_size;

        H5_CHECKED_ASSIGN(size, size_t, temp_size, hsize_t);

    } /* end if */
    else if ( 0 != size % f->shared->fs_page_size )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_CANTINIT, FAIL, \
                    "Page Buffer size must be >= to the page size")

    /* Calculate the minimum page count for metadata and raw data
     * based on the fractions provided 
     */
    min_md_pages = (int32_t)((size * page_buf_min_meta_perc) / 
                             (f->shared->fs_page_size * 100));
    min_rd_pages = (int32_t)((size * page_buf_min_raw_perc) / 
                             (f->shared->fs_page_size * 100));
    HDassert(min_md_pages >= 0);
    HDassert(min_rd_pages >= 0);
    HDassert((min_md_pages + min_rd_pages) <= 
             (int32_t)(size / f->shared->fs_page_size));


    /* compute vfd_swmr_writer */
    if ( ( H5F_VFD_SWMR_CONFIG(f) ) && ( H5F_INTENT(f) & H5F_ACC_RDWR ) ) {

        HDassert(f->shared->vfd_swmr_config.vfd_swmr_writer);
        vfd_swmr_writer = TRUE;
    }


    /* Allocate the new page buffering structure */
    if(NULL == (pb_ptr = H5FL_MALLOC(H5PB_t)))

        HGOTO_ERROR(H5E_PAGEBUF, H5E_NOSPACE, FAIL, "memory allocation failed")

    /* initialize the new instance of H5PB_t */

    pb_ptr->magic            = H5PB__H5PB_T_MAGIC;
    pb_ptr->page_size        = f->shared->fs_page_size;
    H5_CHECKED_ASSIGN(pb_ptr->page_size, size_t, \
                      f->shared->fs_page_size, hsize_t);
    pb_ptr->max_pages        = (int32_t)(size / f->shared->fs_page_size);
    pb_ptr->curr_pages       = 0;
    pb_ptr->curr_md_pages    = 0;
    pb_ptr->curr_rd_pages    = 0;
    pb_ptr->min_md_pages     = min_md_pages;
    pb_ptr->min_rd_pages     = min_rd_pages;

    pb_ptr->max_size         = size;
    pb_ptr->min_meta_perc    = page_buf_min_meta_perc;
    pb_ptr->min_raw_perc     = page_buf_min_raw_perc;

    /* index */
    for ( i = 0; i < H5PB__HASH_TABLE_LEN; i++ )
        pb_ptr->ht[i]        = NULL;
    pb_ptr->index_len        = 0;
    pb_ptr->clean_index_len  = 0;
    pb_ptr->dirty_index_len  = 0;
    pb_ptr->index_size       = 0;
    pb_ptr->clean_index_size = 0;
    pb_ptr->dirty_index_size = 0;
    pb_ptr->il_len           = 0;
    pb_ptr->il_size          = 0;
    pb_ptr->il_head          = NULL;
    pb_ptr->il_tail          = NULL;

    /* LRU */
    pb_ptr->LRU_len          = 0;
    pb_ptr->LRU_size         = 0;
    pb_ptr->LRU_head_ptr     = NULL;
    pb_ptr->LRU_tail_ptr     = NULL;


    /* VFD SWMR specific fields.  
     * The following fields are defined iff vfd_swmr_writer is TRUE. 
     */
    pb_ptr->vfd_swmr_writer  = vfd_swmr_writer;
    pb_ptr->mpmde_count      = 0;
    pb_ptr->cur_tick         = 0;

    /* delayed write list */
    pb_ptr->max_delay        = 0;
    pb_ptr->dwl_len          = 0;
    pb_ptr->dwl_size         = 0;
    pb_ptr->dwl_head_ptr     = NULL;
    pb_ptr->dwl_tail_ptr     = NULL;

    /* tick list */
    pb_ptr->tl_len           = 0;
    pb_ptr->tl_size          = 0;
    pb_ptr->tl_head_ptr      = NULL;
    pb_ptr->tl_tail_ptr      = NULL;

    H5PB_reset_stats(pb_ptr);

    f->shared->pb_ptr = pb_ptr;

    /* if this is a VFD SWMR reader, inform the reader VFD that the 
     * page buffer is configured.  Note that this is for sanity 
     * checking, and only needed until we modify the file open 
     * code to create the page buffer before any file reads in 
     * the VFD SWMR reader case.  After that, this code should be
     * removed.
     *                               JRM -- 1/29/19
     */
    if ( ( H5F_VFD_SWMR_CONFIG(f) ) && 
         ( 0 == (H5F_INTENT(f) & H5F_ACC_RDWR) ) ) {

        HDassert(f->shared->lf);
        HDassert(! f->shared->vfd_swmr_config.vfd_swmr_writer);

        H5FD_vfd_swmr_set_pb_configured(f->shared->lf);
    }

done:

    if ( ret_value < 0 ) {

        if ( pb_ptr != NULL ) {

            pb_ptr = H5FL_FREE(H5PB_t, pb_ptr);

        } 
    } 

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_create */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_dest
 *
 * Purpose:	Flush (if necessary) and evict all entries in the page
 *              buffer, and then discard the page buffer.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/22/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5PB_dest(H5F_t *f)
{
    int i;
    H5PB_t *pb_ptr = NULL;
    H5PB_entry_t *entry_ptr = NULL;
    H5PB_entry_t *evict_ptr = NULL;
    herr_t  ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity check */
    HDassert(f);
    HDassert(f->shared);

    /* flush and destroy the page buffer, if it exists */
    if ( f->shared->pb_ptr ) {

        pb_ptr = f->shared->pb_ptr;

        HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);

        /* the current implementation if very inefficient, and will 
         * fail if there are any outstanding delayed writes -- must fix this 
         */
        for ( i = 0; i < H5PB__HASH_TABLE_LEN; i++ ) {

            entry_ptr = pb_ptr->ht[i];

            while ( entry_ptr ) {

                HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);

                evict_ptr = entry_ptr;
                entry_ptr = entry_ptr->ht_next;

                if ( evict_ptr->is_dirty ) {

                    if ( H5PB__flush_entry(f, pb_ptr, evict_ptr) < 0 )

                        HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                                    "Can't flush entry")
                }

                if ( H5PB__evict_entry(pb_ptr, evict_ptr, TRUE) < 0 )

                    HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                                "forced eviction failed")

                entry_ptr = pb_ptr->ht[i];
            }
        }

        /* regular operations fields */
        HDassert(pb_ptr->curr_pages == 0);
        HDassert(pb_ptr->curr_md_pages == 0);
        HDassert(pb_ptr->curr_rd_pages == 0);
        HDassert(pb_ptr->index_len == 0);
        HDassert(pb_ptr->index_size == 0);
        HDassert(pb_ptr->LRU_len == 0);
        HDassert(pb_ptr->LRU_size == 0);
        HDassert(pb_ptr->LRU_head_ptr == NULL);
        HDassert(pb_ptr->LRU_tail_ptr == NULL);

        /* VFD SWMR fields */
        HDassert(pb_ptr->dwl_len == 0);
        HDassert(pb_ptr->dwl_size == 0);
        HDassert(pb_ptr->dwl_head_ptr == NULL);
        HDassert(pb_ptr->dwl_tail_ptr == NULL);

        HDassert(pb_ptr->tl_len == 0);
        HDassert(pb_ptr->tl_size == 0);
        HDassert(pb_ptr->tl_head_ptr == NULL);
        HDassert(pb_ptr->tl_tail_ptr == NULL);

        pb_ptr->magic = 0;
        f->shared->pb_ptr = H5FL_FREE(H5PB_t, pb_ptr);
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_dest */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_flush
 *
 * Purpose:	If the page buffer is defined, flush all entries.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/22/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5PB_flush(H5F_t *f)
{
    int i;
    H5PB_t *pb_ptr = NULL;
    H5PB_entry_t *entry_ptr = NULL;
    H5PB_entry_t *flush_ptr = NULL;
    herr_t  ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity check */
    HDassert(f);
    HDassert(f->shared);

    pb_ptr = f->shared->pb_ptr;

    if ( pb_ptr ) {

        HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);

        /* the current implementation if very inefficient, and will 
         * fail if there are any delayed writes -- must fix this 
         */
        for ( i = 0; i < H5PB__HASH_TABLE_LEN; i++ ) {

            entry_ptr = pb_ptr->ht[i];

            while ( entry_ptr ) {

                HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);

                flush_ptr = entry_ptr;
                entry_ptr = entry_ptr->ht_next;

                if ( flush_ptr->is_dirty ) {

                    if ( H5PB__flush_entry(f, pb_ptr, flush_ptr) < 0 )

                        HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                                    "Can't flush entry")
                }
            }
        }
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_flush */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_page_exists
 *
 * Purpose:	Test to see if a page buffer page exists at the specified
 *              address.  Set *page_exists_ptr to TRUE or FALSE accordingly.
 *
 *              This function exists for the convenience of the test 
 *              code
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/22/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5PB_page_exists(H5F_t *f, haddr_t addr, hbool_t *page_exists_ptr)
{
    uint64_t page;
    H5PB_t *pb_ptr = NULL;
    H5PB_entry_t *entry_ptr = NULL;
    herr_t  ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity check */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->pb_ptr);

    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(page_exists_ptr);

    /* Calculate the page offset */
    page = (addr / pb_ptr->page_size);

    /* the supplied address should be page aligned */
    HDassert(addr == page * pb_ptr->page_size);

    /* Search for page in the hash table  */
    H5PB__SEARCH_INDEX(pb_ptr, page, entry_ptr, FAIL)

    HDassert((NULL == entry_ptr) || (entry_ptr->addr == addr));

    *page_exists_ptr = ( entry_ptr != NULL );

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_page_exists */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_read
 *
 * Purpose:	Satisfy the read from the page buffer if possible.
 *
 *              1) If the page buffer is disabled, simply read from the 
 *                 HDF5 file and return.
 *
 *              2) If the read is for raw data, and the page buffer is 
 *                 configured for metadata only (i.e. min_md_pages == 
 *                 max_pages), simply read from the HDF5 file and return.
 *
 *              3) If the read is for raw data, and it of page size or 
 *                 larger, read it directly from the HDF5 file.  
 *
 *                 It is possible that the page buffer contains dirty pages 
 *                 that intersect with the read -- test for this and update
 *                 the read buffer from the page buffer if any such pages 
 *                 exist. 
 *
 *                 Note that no pages are inserted into the page buffer in 
 *                 this case.
 *
 *              4) If the read is for raw data, and it is of size less 
 *                 than the page size, satisfy the read from the page 
 *                 buffer, loading and inserting pages into the 
 *                 page buffer as necessary
 *
 *              5) If the read is for metadata, and the page buffer is 
 *                 configured for raw data only (i.e. min_rd_pages == 
 *                 max_pages), simply read from the HDF5 file and return.
 *
 *              The free space manager guarantees that allocations larger
 *              than one page will be page alligned, and that allocations
 *              of size less than or equal to page size will not cross page
 *              boundaries.  Further, unlike raw data, metadata is always 
 *              written and read atomically.
 *
 *              In principle, this should make it easy to discriminate 
 *              between small and multi-page metadata entries so that 
 *              pages containing the former will be buffered and the 
 *              latter be read directly from file.
 *  
 *              Unfortunately, the metadata cache does not always know the 
 *              size of metadata entries when it tries to read them.  In 
 *              such cases, it issues speculative reads that may be either 
 *              smaller or larger than the actual size of the piece of 
 *              metadata that is finally read.
 *
 *              Since we are guaranteed that all metadata allocations larger
 *              that one page are page aligned, we can safely clip at the 
 *              page boundary any non page aligned metadata read that crosses
 *              page boundaries.
 *
 *              However, page aligned reads could wind up being either
 *              small or multi-page.  This results in two scenarios that
 *              we must handle:
 *
 *                  a) A page aligned read of size less than one page 
 *                     turns out to be mult-page.
 *
 *                     In this case, the initial speculative read will
 *                     result in a page load and insertion into the page
 *                     buffer.  This page must be evicted on the subsequent
 *                     read of size greater than page size.
 *
 *                     In the context of VFD SWMR, it is also possible that 
 *                     that the multi-page metadata entry is already in the 
 *                     page buffer -- in which case the initial read should 
 *                     be satisfied from the multi-page page buffer entry.
 *
 *                  b) A page aligned, larger than one page read turns out 
 *                     to be small (less than one page).
 *
 *                     If there is already a page in the page buffer with 
 *                     same address, we can safely clip the original 
 *                     read to page size
 *
 *              The above considerations resolve into the following cases:
 *
 *              6) If the read is for metadata and not page aligned, clip
 *                 the read to the end of the current page if necessary.
 *                 Load the relevant page if necessary and satisfy the 
 *                 read from the page buffer.  Note that it there is an
 *                 existing page, it must not be a multi-page metadata 
 *                 entry.  It it is, flag an error.
 *
 *              7) If the read is for metadata, is page aligned, is larger 
 *                 than one page, and there is no entry in the page buffer,
 *                 satisfy the read from the file
 *
 *              8) If the read is for metadata, is page aligned, is larger 
 *                 than one page, and there is a regular entry at the target
 *                 page address, test to see if the last read was for the 
 *                 same address.
 *
 *                 If was, evict the page, and satisfy the read from file.
 *                 Flag an error if the page was dirty.
 *
 *                 If the last read was for a different page, clip the read 
 *                 to one page, and satisfy the read from the existing 
 *                 regular entry.
 *
 *              9) If the read is for metadata, is page aligned, is larger
 *                 than one page, and there is a multi-page metadata entry
 *                 at the target page address, test to see if 
 *                 pb_ptr->vfd_swmr_write is TRUE.
 *
 *                 If it is, satisfy the read from the multi-page metadata
 *                 entry, clipping the read if necessary.
 *
 *                 if pb_ptr->vfd_swmr_write is FALSE, flag an error.
 *
 *             10) If the read is for metadata, is page aligned, is no 
 *                 larger than a page, test to see if the page buffer 
 *                 contains a page at the target address.
 *
 *                 If it doesn't, load the page and satisfy the read 
 *                 from it.
 *
 *                 If it contains a regular page entry, satisfy the read 
 *                 from it.
 *
 *                 If it contains a multipage metadata entry at the target
 *                 address, satisfy the read from the multi-page metadata
 *                 entry if pb_ptr->vfd_swmr_write is TRUE, and flag an 
 *                 error otherwise.
 *
 *              Observe that this function handles casses 1, 2, and 5
 *              directly, calls H5PB_read_raw() for cases 3 & 4, and 
 *              calls H5PB_read_meta() for cases 6), 7, 8, 9), and 10).
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/11/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
/* TBD Add optional raw-data bypass here and at H5PB_write when we
 * are operating in parallel mode.
 */
herr_t
H5PB_read(H5F_t *f, H5FD_mem_t type, haddr_t addr, size_t size, 
          void *buf/*out*/)
{
    H5PB_t *pb_ptr;                    /* Page buffer for this file */
    hbool_t bypass_pb = FALSE;          /* Whether to bypass page buffering */
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(type != H5FD_MEM_GHEAP);

    pb_ptr = f->shared->pb_ptr;

    if ( pb_ptr == NULL ) {

        bypass_pb = TRUE; /* case 1) -- page buffer is disabled */

    } else {

        HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);

        if ( H5FD_MEM_DRAW == type ) { /* raw data read */

            if ( pb_ptr->min_md_pages == pb_ptr->max_pages ) {

                /* case 2) -- page buffer configured for metadata only */
                bypass_pb = TRUE;

            }
        } else { /* metadata read */

            if ( pb_ptr->min_rd_pages == pb_ptr->max_pages ) {

                /* case 5) -- page buffer configured for raw data only */
                bypass_pb = TRUE;
            }
        }
    }

#ifdef H5_HAVE_PARALLEL
    /* at present, the page buffer must be disabled in the parallel case.
     * However, just in case ...
     */
    if(H5F_HAS_FEATURE(f, H5FD_FEAT_HAS_MPI)) {

        bypass_pb = TRUE;

    } /* end if */
#endif /* H5_HAVE_PARALLEL */

    if ( bypass_pb ) { /* cases 1, 2. and 5 */

#if VFD_IO
        if ( H5FD_read(f->shared->lf, type, addr, size, buf) < 0 ) 
#else /* VFD_IO */
        if ( H5F__accum_read(f, type, addr, size, buf) < 0 )
#endif /* VFD_IO */

            HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                        "read through metadata accumulator failed")

        /* Update statistics */
        if ( pb_ptr ) {

            H5PB__UPDATE_STATS_FOR_BYPASS(pb_ptr, type, size);
        }
    } else {

        if ( H5FD_MEM_DRAW == type ) { /* cases 3 and 4 */

            if ( H5PB__read_raw(f, type, addr, size, buf) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                            "H5PB_read_raw() failed")

        } else { /* cases 6, 7, 8, 9, and 10 */

            if ( H5PB__read_meta(f, type, addr, size, buf) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                            "H5PB_read_meta() failed")
        }

        H5PB__UPDATE_STATS_FOR_ACCESS(pb_ptr, type, size);
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* end H5PB_read() */


/*-------------------------------------------------------------------------
 *
 * Function:    H5PB_remove_entry
 *
 * Purpose:     Remove possible metadata entry with ADDR from the PB cache.
 *
 *              This is in response to the data corruption bug from fheap.c 
 *              with page buffering + page strategy.
 *
 *              Note: Large metadata page bypasses the PB cache.
 *
 *              Note: Update of raw data page (large or small sized) is 
 *                    handled by the PB cache.
 *
 * Return:      Non-negative on success/Negative on failure
 *
 * Programmer:  Vailin Choi; Feb 2017
 *
 * Changes:     Reworked function for re-implementation of the page buffer.
 *
 *              In the context of VFD SWMR, it is possible that the 
 *              discarded page or multi-page metadata entry has been 
 *              modified during the current tick and/or is subject to a 
 *              delayed write.  We must detect this, and remove the entry
 *              from the tick list and/or delayed write list before it is
 *              evicted.
 *
 *              Vailin: I think we need to do this for raw data as well.
 *
 *                                               JRM -- 10/23/18
 *
 *              We also need to evict modified pages from the page 
 *              buffer in the VFD SWMR reader case to avoid message from
 *              the past bugs.  This function will serve for this for 
 *              now, but for efficiency, we may want a version that takes
 *              a list of pages instead.
 *
 *                                               JRM -- 12/30/18
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5PB_remove_entry(const H5F_t *f, haddr_t addr)
{
    uint64_t page;
    H5PB_t *pb_ptr = NULL;
    H5PB_entry_t *entry_ptr = NULL;
    herr_t ret_value = SUCCEED;             /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->pb_ptr);

    pb_ptr = f->shared->pb_ptr;

    /* Calculate the page offset */
    page = (addr / pb_ptr->page_size);

    HDassert(addr == page * pb_ptr->page_size);

    /* Search for page in the hash table */
    H5PB__SEARCH_INDEX(pb_ptr, page, entry_ptr, FAIL)

    if ( entry_ptr ) {

        HDassert(entry_ptr->addr == addr);

        /* A page or a metadata multi-page with vfd_swmr_writer (case 7) */
        HDassert( (entry_ptr->size == pb_ptr->page_size) ||
                  (entry_ptr->size > pb_ptr->page_size && 
                   entry_ptr->mem_type != H5FD_MEM_DRAW &&
                   pb_ptr->vfd_swmr_writer) );

        if ( entry_ptr->modified_this_tick ) {

            H5PB__REMOVE_FROM_TL(pb_ptr, entry_ptr, FAIL);

            entry_ptr->modified_this_tick = FALSE;
        }

        if ( entry_ptr->delay_write_until > 0 ) {

            entry_ptr->delay_write_until = 0;

            H5PB__REMOVE_FROM_DWL(pb_ptr, entry_ptr, FAIL)

            if ( ! ( entry_ptr->is_mpmde ) ) {

                H5PB__UPDATE_RP_FOR_INSERTION(pb_ptr, entry_ptr, FAIL);
            }
        }

        /* if the entry is dirty, mark it clean before we evict */
        if ( ( entry_ptr->is_dirty ) && 
             ( H5PB__mark_entry_clean(pb_ptr, entry_ptr) < 0 ) )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                        "mark entry clean failed")

        if ( H5PB__evict_entry(pb_ptr, entry_ptr, TRUE) < 0 )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, "forced eviction failed")

        /* Do we need to remove the entry from the metadata file index in 
         * the VFD SWMR case?
         *
         * Probably yes -- suppose a page is deallocated, and a multipage
         * metadata entry is allocated at the same base address.  This would
         * change the metadata file entry size.
         *
         * However, this is sufficiently improbably that it doesn't cause
         * problems (that I know of) at present.  
         *
         * Unless it does, hold off on this until we add code to allow entries
         * to age out of the metadata file index, as that will give us the 
         * necessary infrastructure.
         *
         *                                         JRM -- 12/6/18
         */
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_remove_entry */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_update_entry
 *
 * Purpose:	In PHDF5, metadata cache entries that are written by other 
 *              processes are simply marked clean in the current process.
 *              However, if the page buffer is enabled, entries marked
 *              clean must still be written to the page buffer so as to 
 *              keep the contents of metadata pages consistent on all 
 *              processes.
 *
 *              Do this as follows:
 *
 *              1) Test to see if the page buffer is configured to accept
 *                 metadata pages.  If it isn't, return.
 *
 *              2) Test to see if the page buffer contains the page that
 *                 contains the supplied metadata cache entry.  If it 
 *                 doesn't, return.
 *
 *              3) Write the supplied buffer to page at the appropriate 
 *                 offset.
 *
 *              Note that at present, page buffering is disabled in the 
 *              parallel case.  Thus this function has not been tested.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/23/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t 
H5PB_update_entry(H5PB_t *pb_ptr, haddr_t addr, size_t size, const void *buf)
{
    uint64_t page;
    size_t offset;
    H5PB_entry_t *entry_ptr = NULL;
    haddr_t page_addr;
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(size > 0);
    HDassert(size <= pb_ptr->page_size);
    HDassert(buf);

    if ( pb_ptr->min_rd_pages < pb_ptr->max_pages ) {

        /* page buffer is configured to accept metadata pages */

        /* Calculate the aligned address of the containing page */
        page = (addr / pb_ptr->page_size);
        page_addr = page * pb_ptr->page_size;

        H5PB__SEARCH_INDEX(pb_ptr, page, entry_ptr, FAIL)

        if ( entry_ptr ) {

            HDassert( entry_ptr->is_metadata );
            HDassert( ! (entry_ptr->is_mpmde) );
            HDassert(addr + size <= page_addr + pb_ptr->page_size);

            offset = addr - page_addr;

            HDmemcpy(((uint8_t *)(entry_ptr->image_ptr) + offset), 
                     buf, size);

            /* should we mark the page dirty?  If so, replace the following
             * with a call to H5PB__mark_entry_dirty()
             */
            H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)
        }
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_update_entry */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_vfd_swmr__release_delayed_writes
 *
 * Purpose:	After the tick list has been released, and before the 
 *              beginning of the next tick, we must scan the delayed
 *              write list, and release those entries whose delays have
 *              expired.
 *
 *              Note that pages of metadata, and multi-page metadata entries
 *              are handled differently.
 *
 *              Regular pages are removed from the delayed write list and 
 *              inserted in the replacement policy
 *
 *              In contrast, multi-page metadata entries are simply 
 *              flushed and evicted.
 *
 *              Since the delayed write list is sorted in decreasing
 *              delay_write_until order, we start our scan at the bottom
 *              of the delayed write list and continue upwards until no
 *              expired entries remain.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 11/15/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t 
H5PB_vfd_swmr__release_delayed_writes(H5F_t * f)
{
    H5PB_t * pb_ptr = NULL;
    H5PB_entry_t *entry_ptr = NULL;
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->vfd_swmr);
    HDassert(f->shared->vfd_swmr_writer);

    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(pb_ptr->vfd_swmr_writer);

    while ( ( pb_ptr->dwl_tail_ptr ) &&
            ( pb_ptr->dwl_tail_ptr->delay_write_until < 
              f->shared->tick_num ) ) {

        entry_ptr = pb_ptr->dwl_tail_ptr;

        HDassert(entry_ptr->is_dirty);

        entry_ptr->delay_write_until = 0;

        H5PB__REMOVE_FROM_DWL(pb_ptr, entry_ptr, FAIL)

        if ( entry_ptr->is_mpmde ) { /* flush and evict now */
            
            if ( H5PB__flush_entry(f, pb_ptr, entry_ptr) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                            "flush of mpmde failed")

            if ( H5PB__evict_entry(pb_ptr, entry_ptr, TRUE) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                            "eviction of mpmde failed")

        } else { /* insert it in the replacement policy */

            H5PB__UPDATE_RP_FOR_INSERT_APPEND(pb_ptr, entry_ptr, FAIL)
        }
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_vfd_swmr__release_delayed_writes() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_vfd_swmr__release_tick_list
 *
 * Purpose:	After the metadata file has been updated, and before the 
 *              beginning of the next tick, we must release the tick list.
 *
 *              This function performs this function.
 *
 *              In passing, flush and evict any multi-page metadata entries
 *              that are not subject to a delayed write.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 11/12/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t 
H5PB_vfd_swmr__release_tick_list(H5F_t * f)
{
    H5PB_t * pb_ptr = NULL;
    H5PB_entry_t *entry_ptr = NULL;
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->vfd_swmr);
    HDassert(f->shared->vfd_swmr_writer);

    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(pb_ptr->vfd_swmr_writer);

    /* remove all entries from the tick list */
    while ( pb_ptr->tl_head_ptr ) {

        entry_ptr = pb_ptr->tl_head_ptr;

        H5PB__REMOVE_FROM_TL(pb_ptr, entry_ptr, FAIL)

        entry_ptr->modified_this_tick = FALSE;

        if ( entry_ptr->is_mpmde ) {
        
            HDassert(entry_ptr->is_dirty);

            if ( entry_ptr->delay_write_until == 0 ) {

                /* flush and evict the multi-page metadata entry immediately */
                if ( H5PB__flush_entry(f, pb_ptr, entry_ptr) < 0 )

                    HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                                "flush of mpmde failed")

                if ( H5PB__evict_entry(pb_ptr, entry_ptr, TRUE) < 0 )

                    HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                                "eviction of mpmde failed")
            }
        }
        /* if the entry is not a multi-page metadata entry, it must already
         * be on either the replacment policy or the delayed write list.
         * In either case, it will be flush when possible and necessary.
         */
    }

    HDassert(pb_ptr->tl_head_ptr == NULL);
    HDassert(pb_ptr->tl_tail_ptr == NULL);
    HDassert(pb_ptr->tl_len == 0);
    HDassert(pb_ptr->tl_size == 0);

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_vfd_swmr__release_tick_list */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_vfd_swmr__set_tick
 *
 * Purpose:	At the beginning of each tick, the page buffer must be told
 *              to synchronize its copy of the current tick with that of 
 *              the file to which the page buffer belongs.
 *
 *              This function performs this function.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 11/20/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t 
H5PB_vfd_swmr__set_tick(H5F_t * f)
{
    H5PB_t * pb_ptr = NULL;
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->vfd_swmr);
    HDassert(f->shared->vfd_swmr_writer);

    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(pb_ptr->vfd_swmr_writer);

    /* the tick must always increase by 1 -- verify this */
    if ( f->shared->tick_num != pb_ptr->cur_tick + 1 )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                    "f->shared->tick_num != pb_ptr->cur_tick + 1 ?!?!")

    pb_ptr->cur_tick = f->shared->tick_num;

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_vfd_swmr__release_tick_list */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_vfd_swmr__update_index
 *
 * Purpose:	In the VFD SWMR writer, all metadata writes to the page 
 *              buffer during a tick are buffered in the page buffer in 
 *              the tick list.  Further, the metadata cache is flushed 
 *              to the page buffer at the end of the tick so that all 
 *              metadata changes during the tick are reflected in the 
 *              tick list.
 *
 *              Once this is done, the internal representation of the 
 *              metadata file index must be updated from the tick list 
 *              so that the metadata file can be updated, and the tick 
 *              list can be emptied and prepared to buffer metadata changes
 *              in the next tick.
 *
 *              This function is called to accomplish this.  Its cycle of
 *              operation is as follows:
 *
 *              1) Scan the tick list.  For each entry (*pbe_ptr), test 
 *                 to see if it appears in the index.
 *
 *                 If it does the entry must have been modified in the 
 *                 past tick.  Update the index entry (*ie_ptr) as follows:
 *
 *                 a) Set ie_ptr->entry_ptr = pbe_ptr->image_ptr.  This 
 *                    is needed to give the metadata file update code 
 *                    access to the image of the target page or multi-page
 *                    multi-date entry.  Note that ie_ptr->entry_ptr will
 *                    be set to NULL as soon as the metadata file is updated,
 *                    so the buffer pointed to by pbe_ptr->image_ptr can 
 *                    be safely discarded at any time after the metadata 
 *                    file update.
 *
 *                 b) Set ie_ptr->tick_of_last_change to the current tick.
 *
 *                 c) If pbe_ptr->is_dirty, set ie_ptr->clean to FALSE.
 *                    If pbe_ptr->is_dirty is FALSE, set ie_ptr->clean
 *                    to TRUE and set ie_ptr->tick_of_last_flush to the 
 *                    current tick.
 *
 *                 If the tick list entry (*pbe_ptr) doesn't appear in 
 *                 the index, allocate a metadata file index entry (*ie_ptr), 
 *                 and initialize it as follows:
 *
 *                     ie_ptr->hdf5_page_offset = pbe_ptr->page
 *                     ie_ptr->length           = pbe_ptr->size
 *                     ie_ptr->delayed_flush    = pbe_ptr->delay_write_until
 * 
 *                 and then update the new entry as per the existing entry
 *                 case described above.
 *
 *              2) Scan the internal representation of the metadata file 
 *                 index for entries that do not appear in the tick list.
 *                 For each such entry (*ie_ptr), proceed as follows:
 *
 *                 1) If ie_ptr->clean, we are done -- proceed to the 
 *                    next index entry that doesn't appear in the tick list.
 *
 *                 2) Test to see if the cognate entry appears in the page 
 *                    buffer.  If it doesn't, it must have been flushed and
 *                    evicted in the past tick.  Set
 *
 *                        ie_ptr->clean = TRUE, and 
 *
 *                        ie_ptr->tick_of_last_flush = current tick
 *
 *                    and proceed to the next index entry that doesn't 
 *                    appear in the tick list.
 *
 *                 3) If the cognate entry does appear in the page buffer
 *                    and is clean, proceed as per 2) above.
 *
 *                 4) In all other cases, do nothing, and proceed to the 
 *                    next index entry that does not appear in the tick list.
 *
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 11/9/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t 
H5PB_vfd_swmr__update_index(H5F_t * f, 
                            uint32_t * idx_ent_added_ptr, 
                            uint32_t * idx_ent_modified_ptr,
                            uint32_t * idx_ent_not_in_tl_ptr,
                            uint32_t * idx_ent_not_in_tl_flushed_ptr)
{
    uint32_t i;
    uint32_t idx_ent_added = 0;
    uint32_t idx_ent_modified = 0;
    uint32_t idx_ent_not_in_tl = 0;
    uint32_t idx_ent_not_in_tl_flushed = 0;
    H5PB_t * pb_ptr = NULL;
    H5PB_entry_t *pbe_ptr = NULL;
    H5FD_vfd_swmr_idx_entry_t * ie_ptr = NULL;
    H5FD_vfd_swmr_idx_entry_t * idx = NULL;
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->vfd_swmr);
    HDassert(f->shared->vfd_swmr_writer);

    idx = f->shared->mdf_idx;

    HDassert(idx);
    
    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(pb_ptr->vfd_swmr_writer);

    HDassert(idx_ent_added_ptr);
    HDassert(idx_ent_modified_ptr);
    HDassert(idx_ent_not_in_tl_ptr);
    HDassert(idx_ent_not_in_tl_flushed_ptr);

    /* scan the tick list and insert or update metadata file index entries 
     * as appropriate.
     */

    pbe_ptr = pb_ptr->tl_head_ptr;
    
    while ( pbe_ptr ) {

        uint64_t target_page;
        int32_t top;
        int32_t bottom;
        int32_t probe;

        HDassert(pbe_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);

        /* do a binary search on the metadata file index to see if 
         * it already contains an entry for *pbe_ptr.
         */

        ie_ptr = NULL; 
        top = f->shared->mdf_idx_entries_used - 1;
        bottom = 0;
        target_page = pbe_ptr->page;
        
        while ( top >= bottom ) {

            probe = (top + bottom) / 2;

            if ( idx[probe].hdf5_page_offset < target_page ) {

                bottom = probe + 1;

            } else if ( idx[probe].hdf5_page_offset > target_page ) {

                top = probe - 1;

            } else { /* found it */

                ie_ptr = idx + probe;
                bottom = top + 1; /* to exit loop */
            }
        }

        if ( ie_ptr == NULL ) { /* alloc new entry in the metadata file index*/

            /* for now the metadata file index is of fixed size -- if we 
             * exceed the maximum size, just abort.
             *
             * Obviously, this must be fixed for the production version.
             */
            uint32_t new_index_entry_index;

            new_index_entry_index = f->shared->mdf_idx_entries_used + 
                                    idx_ent_added++;

            if ( new_index_entry_index >= f->shared->mdf_idx_len ) {

                HDfprintf(stderr, "\n\nmax mdf index len (%d)exceeded.\n\n",
                          f->shared->mdf_idx_len);
                HDfprintf(stderr, "tick = %lld.\n", f->shared->tick_num);
                exit(1);
            }

            ie_ptr = idx + new_index_entry_index;

            /* partial initialization of new entry -- rest done later */
            ie_ptr->hdf5_page_offset     = target_page;
            ie_ptr->md_file_page_offset  = 0; /* undefined at this point */
            ie_ptr->length               = (uint32_t)(pbe_ptr->size);
            ie_ptr->chksum               = 0; /* undefined at this point */
            /* ie_ptr->entry_ptr            initialized below */
            /* ie_ptr->tick_of_last_change  initialized below */
            /* ie_ptr->clean                initialized below */
            /* ie_ptr->tick_of_last_flush   initialized below */
            ie_ptr->delayed_flush        = pbe_ptr->delay_write_until;
            ie_ptr->moved_to_hdf5_file   = FALSE;

        } else {

            idx_ent_modified++;
        }

        ie_ptr->entry_ptr            = pbe_ptr->image_ptr;
        ie_ptr->tick_of_last_change  = f->shared->tick_num;
        ie_ptr->clean                = !(pbe_ptr->is_dirty);

        if ( ie_ptr->clean ) {

            ie_ptr->tick_of_last_flush = f->shared->tick_num;

        } else {

            ie_ptr->tick_of_last_flush = 0;
        }

        HDassert(ie_ptr);

        pbe_ptr = pbe_ptr->tl_next;
    }

    /* scan the metadata file index for entries that don't appear in the 
     * tick list.  If the index entry is dirty, and either doesn't appear
     * in the page buffer, or is clean in the page buffer, mark the index
     * entry clean and as having been flushed in the current tick.
     */
    for ( i = 0; i < f->shared->mdf_idx_entries_used; i++ ) {

        HDassert( ( i == 0 ) || 
                  ( idx[i - 1].hdf5_page_offset < idx[i].hdf5_page_offset ) );

        if ( idx[i].tick_of_last_change < f->shared->tick_num ) {

            idx_ent_not_in_tl++;

            ie_ptr = idx + i;

            if ( ! ( ie_ptr->clean ) ) {

                H5PB__SEARCH_INDEX(pb_ptr, ie_ptr->hdf5_page_offset, \
                                   pbe_ptr, FAIL);

                if ( ( ! pbe_ptr ) || ( ! ( pbe_ptr->is_dirty ) ) ) {

                    idx_ent_not_in_tl_flushed++;
                    ie_ptr->clean = TRUE;
                    ie_ptr->tick_of_last_flush = f->shared->tick_num;
                }
            }
        }
    }

    HDassert(idx_ent_modified + idx_ent_not_in_tl == 
             f->shared->mdf_idx_entries_used);

    HDassert(idx_ent_modified + idx_ent_not_in_tl + idx_ent_added <=
             f->shared->mdf_idx_len);

    *idx_ent_added_ptr             = idx_ent_added;
    *idx_ent_modified_ptr          = idx_ent_modified;
    *idx_ent_not_in_tl_ptr         = idx_ent_not_in_tl;
    *idx_ent_not_in_tl_flushed_ptr = idx_ent_not_in_tl_flushed;

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_vfd_swmr__update_index */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB_write
 *
 * Purpose:	Write data into the Page Buffer if practical, and to file
 *              otherwise.  Specifically:
 *
 *              1) If the page buffer is disabled, simply write to the 
 *                 HDF5 file and return.
 *
 *              2) If the write is raw data, and the page buffer is 
 *                 configured for metadata only (i.e. min_md_pages == 
 *                 max_pages), simply write to the HDF5 file and return.
 *
 *              3) If the write is raw data, and it of page size or 
 *                 larger, write directly from the HDF5 file.  
 *
 *                 It is possible that the write intersects one or more 
 *                 pages in the page buffer -- test for this and update
 *                 any partially written pages, and evict any pages 
 *                 that are completely overwritten.
 *
 *                 Note that no pages are inserted into the page buffer in 
 *                 this case.
 *
 *              4) If the write is of raw data, and it is of size less 
 *                 than the page size, write the page into the page
 *                 buffer, loading and inserting pages into the 
 *                 page buffer as necessary
 *
 *              5) If the write is of metadata, and the page buffer is 
 *                 configured for raw data only (i.e. min_rd_pages == 
 *                 max_pages), simply write to the HDF5 file and return.
 *
 *              6) If the write is of metadata, the write is larger than
 *                 one page, and vfd_swmr_writer is FALSE, simply read 
 *                 from the HDF5 file.  There is no need to check the 
 *                 page buffer, as metadata is always read atomically, 
 *                 and entries of this size are not buffered in the page 
 *                 buffer.
 *
 *              7) If the write is of metadata, the write is larger than
 *                 one page, and vfd_swmr_writer is TRUE, the write must
 *                 buffered in the page buffer until the end of the tick.
 *
 *                 If it doesn't exist already, create a multi-page metadata 
 *                 entry in the page buffer and copy the write into it.  
 *                 Insert the new entry in the tick list if necessary.
 *
 *                 Test to see if the write of the multi-page metadata 
 *                 entry must be delayed.  If so, place the entry in 
 *                 the delayed write list.  Otherwise, the multi-page
 *                 metadata entry will be written to the HDF5 file and
 *                 evicted when the tick list is released at the of the 
 *                 tick.
 *
 *
 *              8) If the write is of metadata, and the write is of size
 *                 less than or equal to the page size, write the data
 *                 into the page buffer, loading and inserting a page 
 *                 if necessary.
 *
 *                 If, in addition, vfd_swmr_writer is TRUE, add the page
 *                 touched by the write to the tick list.
 *                 
 *              Observe that this function handles casses 1, 2, 5, and 6 
 *              directly, calls H5PB_write_raw() for cases 3 & 4, and 
 *              calls H5PB_read_meta() for cases 7, and 8.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/11/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5PB_write(H5F_t *f, H5FD_mem_t type, haddr_t addr, size_t size, 
           const void *buf)
{
    H5PB_t *pb_ptr;                    /* Page buffer for this file */
    hbool_t bypass_pb = FALSE;          /* Whether to bypass page buffering */
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(type != H5FD_MEM_GHEAP);

    pb_ptr = f->shared->pb_ptr;

    if ( pb_ptr == NULL ) {

        bypass_pb = TRUE; /* case 1) -- page buffer is disabled */

    } else {

        HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);

        if ( H5FD_MEM_DRAW == type ) { /* raw data write */

            if ( pb_ptr->min_md_pages == pb_ptr->max_pages ) {

                /* case 2) -- page buffer configured for metadata only */
                bypass_pb = TRUE;

            }
        } else { /* metadata write */

            if ( pb_ptr->min_rd_pages == pb_ptr->max_pages ) {

                /* case 5) -- page buffer configured for raw data only */
                bypass_pb = TRUE;

            } else if ( ( size >= pb_ptr->page_size ) && 
                        ( ! ( pb_ptr->vfd_swmr_writer ) ) ) {

                /* case 6) -- md read larger than one page and 
                 *            pb_ptr->vfd_swmr_writer is FALSE.
                 */
                bypass_pb = TRUE;
            }
        }
    }

#ifdef H5_HAVE_PARALLEL
    /* at present, the page buffer must be disabled in the parallel case.
     * However, just in case ...
     */
    if(H5F_HAS_FEATURE(f, H5FD_FEAT_HAS_MPI)) {

        bypass_pb = TRUE;

    } /* end if */
#endif /* H5_HAVE_PARALLEL */

    if ( bypass_pb ) { /* cases 1, 2. 5, and 6 */

#if VFD_IO
        if ( H5FD_write(f->shared->lf, type, addr, size, buf) < 0 )
#else /* VFD_IO */
        if ( H5F__accum_write(f, type, addr, size, buf) < 0 )
#endif /* VFD_IO */

            HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                        "write through metadata accumulator failed")

        /* Update statistics */
        if ( pb_ptr ) {

            H5PB__UPDATE_STATS_FOR_BYPASS(pb_ptr, type, size);
        }
    } else {

        if ( H5FD_MEM_DRAW == type ) { /* cases 3 and 4 */

            if ( H5PB__write_raw(f, type, addr, size, buf) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                            "H5PB_read_raw() failed")

        } else { /* cases 7, and 8 */

            if ( H5PB__write_meta(f, type, addr, size, buf) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                            "H5PB_read_meta() failed")
        }

        H5PB__UPDATE_STATS_FOR_ACCESS(pb_ptr, type, size);
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* end H5PB_write() */


/**************************************************************************/
/***************************** STATIC FUNCTIONS ***************************/
/**************************************************************************/

/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__allocate_page
 *
 * Purpose:	Allocate an instance of H5PB_entry_t and its associated
 *              buffer.  The supplied size must be greater than or 
 *              equal to pb_ptr->page_size, and equal to that value if 
 *              pb_ptr->vfd_swmr_writer is FALSE.
 *
 *              The associated buffer is zeroed if clean_image is TRUE.
 *
 * Return:	Pointer to the newly allocated instance of H5PB_entry_t
 *              on success, and NULL on failure.
 *
 * Programmer:	John Mainzer -- 10/12/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static H5PB_entry_t *
H5PB__allocate_page(H5PB_t *pb_ptr, size_t size, hbool_t clean_image)
{
    H5PB_entry_t *entry_ptr = NULL;
    void * image_ptr = NULL; 
    H5PB_entry_t *ret_value = NULL;    /* Return value */

    FUNC_ENTER_NOAPI(NULL)

    /* sanity checks */
    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(size >= pb_ptr->page_size);
    HDassert((size == pb_ptr->page_size) || (pb_ptr->vfd_swmr_writer));

    /* allocate the entry and its associated image buffer */
    if ( NULL == (entry_ptr = H5FL_MALLOC(H5PB_entry_t)))

        HGOTO_ERROR(H5E_PAGEBUF, H5E_NOSPACE, NULL, \
                    "memory allocation for H5PB_entry_t failed")

    if ( clean_image ) {

        image_ptr = H5MM_calloc(size);

    } else {

        image_ptr = H5MM_malloc(size);
    }

    if ( NULL == image_ptr )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_NOSPACE, NULL, \
                    "memory allocation for page image failed")

    /* initialize the new page buffer entry */
    entry_ptr->magic              = H5PB__H5PB_ENTRY_T_MAGIC;
    entry_ptr->pb_ptr             = pb_ptr;
    entry_ptr->addr               = HADDR_UNDEF;
    entry_ptr->page               = 0;
    entry_ptr->size               = size;
    entry_ptr->image_ptr          = image_ptr;
    entry_ptr->mem_type           = H5FD_MEM_DEFAULT;
    entry_ptr->is_metadata        = FALSE;
    entry_ptr->is_mpmde           = FALSE;
    entry_ptr->is_dirty           = FALSE;

    /* fields supporting the hash table */
    entry_ptr->ht_prev            = NULL;
    entry_ptr->ht_next            = NULL;
    entry_ptr->il_prev            = NULL;
    entry_ptr->il_next            = NULL;

    /* fields supporting replacement policise */
    entry_ptr->next               = NULL;
    entry_ptr->prev               = NULL;

    /* fields supporting VFD SWMR */
    entry_ptr->is_mpmde           = FALSE;
    entry_ptr->loaded             = FALSE;
    entry_ptr->modified_this_tick = FALSE;
    entry_ptr->delay_write_until  = 0;
    entry_ptr->tl_next            = NULL;
    entry_ptr->tl_prev            = NULL;

    ret_value = entry_ptr;

done:

    if ( NULL == ret_value ) {

        if ( entry_ptr ) {

            entry_ptr->magic = 0;
            entry_ptr = H5FL_FREE(H5PB_entry_t, entry_ptr);
        }

        if ( image_ptr ) {

            image_ptr = H5MM_xfree(image_ptr);
        }
    } /* end if */

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB__allocate_page() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__create_new_page
 *
 * Purpose:	Create a new page and insert it in the page buffer with 
 *              the specified address and type.  If entry_ptr_ptr is not
 *              NULL, return a pointer to the new entry in *entry_ptr_ptr.
 *
 *              Throw an error if a page already exists at the specified
 *              address.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/12/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
herr_t 
H5PB__create_new_page(H5PB_t *pb_ptr, haddr_t addr, size_t size, 
    H5FD_mem_t type, hbool_t clean_image, H5PB_entry_t **entry_ptr_ptr)
{
    hbool_t inserted_in_index = FALSE;
    hbool_t inserted_in_lru = FALSE;
    uint64_t page;
    H5PB_entry_t *entry_ptr = NULL;
    herr_t ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);

    page = (uint64_t)addr / (uint64_t)(pb_ptr->page_size);

    HDassert((uint64_t)(addr) == (page * (uint64_t)(pb_ptr->page_size)));

    HDassert(size >= pb_ptr->page_size);
    HDassert((size == pb_ptr->page_size) || 
             ((pb_ptr->vfd_swmr_writer) && (type != H5FD_MEM_DRAW)));
    HDassert((NULL == entry_ptr_ptr) || (NULL == *entry_ptr_ptr));

    H5PB__SEARCH_INDEX(pb_ptr, page, entry_ptr, FAIL);

    if ( entry_ptr != NULL ) {

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
            "page buffer already contains a page at the specified address")
    } 

    entry_ptr = H5PB__allocate_page(pb_ptr, size, clean_image);

    if ( NULL == entry_ptr )
        HGOTO_ERROR(H5E_PAGEBUF, H5E_NOSPACE, FAIL, \
                    "Can't allocate new page buffer entry")

    /* perform additional initialization */
    HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
    HDassert(entry_ptr->pb_ptr == pb_ptr);
    entry_ptr->addr        = addr;
    entry_ptr->page        = page;
    HDassert(entry_ptr->size == size);
    HDassert(entry_ptr->image_ptr);
    entry_ptr->mem_type    = type;
    entry_ptr->is_metadata = (type != H5FD_MEM_DRAW);
    entry_ptr->is_mpmde    = ((entry_ptr->is_metadata) &&
                              (size > pb_ptr->page_size));
    entry_ptr->is_dirty    = FALSE;

    /* insert in the hash table */
    H5PB__INSERT_IN_INDEX(pb_ptr, entry_ptr, FAIL)
    inserted_in_index = TRUE; 

    /* insert at the head of the LRU if it isn't a multi-page metadata entry */
    if ( ! entry_ptr->is_mpmde ) {

        H5PB__UPDATE_RP_FOR_INSERTION(pb_ptr, entry_ptr, FAIL)
        inserted_in_lru = TRUE;
    }

    /* updates stats */
    H5PB__UPDATE_STATS_FOR_INSERTION(pb_ptr, entry_ptr);

    if ( entry_ptr_ptr ) {

        *entry_ptr_ptr = entry_ptr;
    }

done:

    if ( ret_value < 0 ) {

        if ( entry_ptr ) {

            if ( inserted_in_lru ) {

                H5PB__UPDATE_RP_FOR_EVICTION(pb_ptr, entry_ptr, FAIL);
            }

            if ( inserted_in_index ) {

                H5PB__DELETE_FROM_INDEX(pb_ptr, entry_ptr, FAIL)
            }

            H5PB__deallocate_page(entry_ptr);
            entry_ptr = NULL;
        }
    }

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB_add_new_page */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__deallocate_page
 *
 * Purpose:	Free the supplied instance of H5PB_entry_t and its 
 *              associated buffer.  The entry must be clean and removed 
 *              from the page buffer before this function is called.
 *
 * Return:	void
 *
 * Programmer:	John Mainzer -- 10/12/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static void 
H5PB__deallocate_page(H5PB_entry_t *entry_ptr)
{
    FUNC_ENTER_NOAPI_NOINIT_NOERR

    /* sanity checks */
    HDassert(entry_ptr);
    HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
    HDassert(entry_ptr->size > 0);
    HDassert(entry_ptr->image_ptr);
    HDassert(!(entry_ptr->is_dirty));
    HDassert(entry_ptr->ht_next == NULL);
    HDassert(entry_ptr->ht_prev == NULL);
    HDassert(entry_ptr->il_next == NULL);
    HDassert(entry_ptr->il_prev == NULL);
    HDassert(entry_ptr->next == NULL);
    HDassert(entry_ptr->prev == NULL);
    HDassert(entry_ptr->tl_next == NULL);
    HDassert(entry_ptr->tl_prev == NULL);

    entry_ptr->magic = 0;
    entry_ptr->image_ptr = H5MM_xfree(entry_ptr->image_ptr);
    entry_ptr = H5FL_FREE(H5PB_entry_t, entry_ptr);

    FUNC_LEAVE_NOAPI_VOID

} /* H5PB__deallocate_page() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__evict_entry
 *
 * Purpose:	Evict the target entry from the from the page buffer, and 
 *              de-allocate its associated image and instance of 
 *              H5PB_entry_t.
 *
 *              In general, entries must be clean before they can be 
 *              evicted, and the minimum metadata and raw data limits 
 *              must be respected.  Attempts to evict an entry that 
 *              that do not respect these constraints will generate 
 *              and error unless the force parameter is TRUE, in which
 *              case, these constraints are igmored.
 *
 *              In the context of VFD SWMR, there is also the requirement
 *              that entries to be evicted not be on the tick list, and
 *              also not reside on the delayed write list.  In the rare
 *              case in which such a page is discarded by the free space
 *              manager, it must be removed from the tick list and/or the
 *              delayed write list before being evicted by this function.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/14/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__evict_entry(H5PB_t *pb_ptr, H5PB_entry_t *entry_ptr, hbool_t force)
{
    herr_t ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* sanity checks */
    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(entry_ptr);
    HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
    HDassert(entry_ptr->size > 0);
    HDassert(entry_ptr->image_ptr);
    /* entries on either the tick list or the delayed write 
     * list may not be evicted -- verify this.
     */
    HDassert(!(entry_ptr->modified_this_tick));
    HDassert(entry_ptr->delay_write_until == 0);

    if ( ( ! force ) && ( entry_ptr->is_dirty ) )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                    "Attempt to evict a dirty entry");

    if ( ! force ) {

        /* it is OK to evict an metadata page if pb_ptr->curr_md_pages ==
         * pb_ptr->min_md_pages - 1 if we are about to replace it with another
         * metadata page.  
         *
         * Similarly, it is OK to evict an raw data page if 
         * pb_ptr->curr_rd_pages == pb_ptr->min_rd_pages - 1 if we are 
         * about to replace it with another raw data page.  
         * 
         * Assume sanity checks have been made before this call, and 
         * allow the above without testing the intended replacement.
         */
        if ( ( entry_ptr->is_metadata ) &&
             ( pb_ptr->curr_md_pages < pb_ptr->min_md_pages ) ) {

            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                        "Attempt to violate min_md_pages");

        } else if ( ( ! entry_ptr->is_metadata ) &&
                    ( pb_ptr->curr_rd_pages < pb_ptr->min_rd_pages ) ) {

            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                        "Attempt to violate min_rd_pages");
        } 
    } else if ( ( entry_ptr->is_dirty ) && 
                ( H5PB__mark_entry_clean(pb_ptr, entry_ptr) < 0 ) ) {

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, "mark entry clean failed")
    }

    /* if the entry is in the replacement policy, remove it */
    if ( ! (entry_ptr->is_mpmde) ) {

        H5PB__UPDATE_RP_FOR_EVICTION(pb_ptr, entry_ptr, FAIL)
    }

    /* remove the entry from the hash table */
    H5PB__DELETE_FROM_INDEX(pb_ptr, entry_ptr, FAIL)

    /* update stats for eviction */
    H5PB__UPDATE_STATS_FOR_EVICTION(pb_ptr, entry_ptr)

    /* deallocate the page */
    H5PB__deallocate_page(entry_ptr);

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB__evict_entry() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__flush_entry
 *
 * Purpose:	Flush the target entry to file.
 *
 *              Under normal circumstances, the entry will be in the 
 *              replacement policy.  In this, also update the replacement
 *              policy for flush.
 *
 *              If pb_ptr->vfd_swmr_writer, it is possible that the target
 *              is a multi-page metadata entry.  In this case, the entry
 *              is not in the replacement policy, and thus the policy 
 *              should not be updated.
 *              
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/14/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__flush_entry(H5F_t *f, H5PB_t *pb_ptr, H5PB_entry_t *entry_ptr)
{
    hbool_t skip_write = FALSE;
    size_t write_size;
    haddr_t eoa;                   /* Current EOA for the file */
#if VFD_IO  /* JRM */
    H5FD_t *file;                  /* file driver */
#endif /* VFD_IO */ /* JRM */
    herr_t ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->lf);
    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(entry_ptr);
    HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
    HDassert(entry_ptr->size > 0);
    HDassert(entry_ptr->size >= pb_ptr->page_size);
    HDassert((entry_ptr->size == pb_ptr->page_size) || (entry_ptr->is_mpmde));
    HDassert(entry_ptr->image_ptr);
    HDassert(entry_ptr->is_dirty);
    HDassert((pb_ptr->vfd_swmr_writer) || (!(entry_ptr->is_mpmde)));
    HDassert((uint64_t)0 == (entry_ptr->delay_write_until));

    /* Retrieve the 'eoa' for the file */
    if ( HADDR_UNDEF == (eoa = H5F_get_eoa(f, entry_ptr->mem_type)) )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_CANTGET, FAIL, \
                    "driver get_eoa request failed")

    /* TODO: update the free space manager to inform the page buffer when 
     *       space is de-allocated so that the following assertions will be
     *       true in all cases.
     */

    /* Verify that the base addresss of the page is within the EOA.  If it 
     * isn't, the associated page has been discarded and should have been 
     * removed from the page buffer.  This is a bug in the HDF5 library, so 
     * an assertion is adequate here.
     */
    HDassert( eoa > entry_ptr->addr );

    /* Space at the end of the file should be allocate in increments of 
     * pages.  Thus the entire page should be within the EOA.  Again,
     * an assertion is adequate here.
     */
    HDassert( eoa >= entry_ptr->addr + entry_ptr->size );
    
    write_size = entry_ptr->size;

    /* flush the entry */
    if ( ! skip_write ) {
#if VFD_IO  /* JRM */
        file = f->shared->lf;

        if ( H5FD_write(file, entry_ptr->mem_type, entry_ptr->addr, 
                        write_size, entry_ptr->image_ptr) < 0 )
#else /* VFD_IO */ /* JRM */
        if ( H5F__accum_write(f, entry_ptr->mem_type, entry_ptr->addr, 
                              write_size, entry_ptr->image_ptr) < 0 )
#endif /* VFD_IO */ /* JRM */

            HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, "file write failed")
    }

    /* mark the entry clean */
    if ( H5PB__mark_entry_clean(pb_ptr, entry_ptr) < 0 )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, "mark entry clean failed")


    /* if the entry is on the LRU, update the replacement policy */
    if ( ( ! (entry_ptr->is_mpmde) ) && 
         ( entry_ptr->delay_write_until == 0 ) ) {

        H5PB__UPDATE_RP_FOR_FLUSH(pb_ptr, entry_ptr, FAIL)        
    }

    /* update stats for flush */
    H5PB__UPDATE_STATS_FOR_FLUSH(pb_ptr, entry_ptr)

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB__flush_entry() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__load_page
 *
 * Purpose:	Load the page with the specified base address and insert
 *              it into the page buffer.  If necessary and possible, make 
 *              space for the new page first.
 *
 *              Note that the size of the page is always pb_ptr->page_size,
 *              even in the VFD SWMR case, as in this context, multi-page 
 *              metadata entries are always written in full, and they 
 *              may only enter the page buffer as the result of a write.
 *
 *              In the context of VFD SWMR, when an page is loaded from 
 *              file, it is possible that the VFD SWMR writer must delay 
 *              writes to the page to avoid the possibility of message from 
 *              the future bugs on the VFD SWMR reader.  For this reason,
 *              make note of the fact that the entry has be loaded from 
 *              from file, so that the necessary checks can be made when
 *              writing to the page.
 *              
 * Return:	SUCCEED if no errors are encountered, and 
 *              FAIL otherwise.
 *
 * Programmer:	John Mainzer -- 10/18/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__load_page(H5F_t *f, H5PB_t *pb_ptr, haddr_t addr, H5FD_mem_t type,
    H5PB_entry_t **entry_ptr_ptr)
{
    hbool_t skip_read = FALSE;
    haddr_t eoa;
    haddr_t eof = HADDR_UNDEF;
    H5PB_entry_t *entry_ptr = NULL;
    void *image_ptr = NULL;
#if VFD_IO /* JRM */
    H5FD_t *file;                       /* File driver pointer */
#endif /* VFD_IO */ /* JRM */
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->lf);
    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert((entry_ptr_ptr == NULL) || (*entry_ptr_ptr == NULL));

    /* Retrieve the 'eoa' for the file */
    if ( HADDR_UNDEF == (eoa = H5F_get_eoa(f, type)))

        HGOTO_ERROR(H5E_PAGEBUF, H5E_CANTGET, FAIL, \
                    "driver get_eoa request failed")
#if 0 /* JRM */
    if ( addr + ((haddr_t)(pb_ptr->page_size)) > eoa )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                    "Attempt to load page that extends past EOA")
#endif /* JRM */
    if ( HADDR_UNDEF == (eof = H5FD_get_eof(f->shared->lf, H5FD_MEM_DEFAULT)) )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_CANTGET, FAIL, \
                    "driver get_eof request failed")

    /* It is possible that this page been allocated but not
     * written.  Skip the read if addr > EOF.  In this case, tell 
     * H5PB__create_new_page() to zero the page image.
     *
     * Don't set "skip_read = (addr >= eof);" when accumulator is used.
     */
#if VFD_IO /* JRM */
    skip_read = (addr >= eof);
#endif /* VFD_IO */ /* JRM */

    /* make space in the page buffer if necessary */
    if ( ( pb_ptr->curr_pages >= pb_ptr->max_pages ) &&
         ( H5PB__make_space(f, pb_ptr, type) < 0 ) )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                    "H5PB__make_space() reports an error")


    /* Create a new page buffer page and insert it into the page buffer */
    if ( H5PB__create_new_page(pb_ptr, addr, (size_t)(pb_ptr->page_size), 
                               type, skip_read, &entry_ptr) < 0 )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                    "can't create new page buffer page")

    HDassert(entry_ptr);
    HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
    HDassert(entry_ptr->addr == addr);

    image_ptr = entry_ptr->image_ptr;

    HDassert(image_ptr);

    /* Read the contents of the page from file, and store it in the 
     * image buffer associated with the new entry.
     */
#if VFD_IO /* JRM */
    file = f->shared->lf;
    if ( ( ! skip_read ) &&
         ( H5FD_read(file, type, addr, entry_ptr->size, image_ptr) < 0 ) )
#else /* VFD_IO */ /* JRM */
    if ( ( ! skip_read ) &&
         ( H5F__accum_read(f, type, addr, entry_ptr->size, image_ptr) < 0 ) )
#endif /* VFD_IO */ /* JRM */

        HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                    "driver read request failed")

    /* If in fact the page was read from file, make note of this fact
     * for purposes of VFD SWMR delayed writes in the VFD SWMR writer.
     */
    entry_ptr->loaded = ! skip_read;

    H5PB__UPDATE_STATS_FOR_LOAD(pb_ptr, entry_ptr)

    if ( entry_ptr_ptr ) {

        *entry_ptr_ptr = entry_ptr;
    }

done:

    /* add cleanup in case of failure */

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB__load_page() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__make_space
 *
 * Purpose:	Evict one or more pages from the page buffer so as to 
 *              reduce the size of the page buffer to pb_ptr->max_pages - 1.
 *              if possible.
 *
 *              Note that the function must not be called under 
 *              non-sencicle conditions -- thus if either 
 *
 *                  1) the inserted type is metadata and min_rd_pages ==
 *                     max_pages, or 
 *
 *                  2) the inserted type is raw data and min_md_pages ==
 *                     max_pages
 *              
 *              holds, the function has been called in error, and an 
 *              assertion failure is appropriate.
 *
 *              If the page buffer is below its maximum size, we are 
 *              done, and the function simply returns.
 *
 *              Otherwise, scan upwards from the bottom of the LRU list, 
 *              examining each entry in turn.
 *
 *              If the entry is dirty, flush it, move it to the top of the 
 *              LRU, and continue with the scan.  Note in the VFD SWMR case,
 *              we do not have to concern ourselves with delayed writes in 
 *              this context, as all entries which are subject to delayed 
 *              writes must reside on the delayed write list, not the LRU list.
 *
 *              If the entry is:
 *
 *                 1) clean
 *
 *                 2) either: 
 *
 *                    a) the target entry is metadata and 
 *                       curr_md_pages > min_md_pages.
 *
 *                    b) the target entry is raw data and 
 *                       curr_rd_pages > min_rd_pages.
 *
 *                    c) the target entry is metadata, the inserted_type
 *                       is metadata, and curr_md_pages == min_md_pages.
 *
 *                    d) the target entry is raw data, the inserted_type
 *                       is raw data, and curr_rd_pages == min_rd_pages.
 *
 *                 3) The entry is not on the tick list (which can only 
 *                    happen if pb_ptr->vfd_swmr_writer is TRUE).
 *
 *              evict the entry and test to see if pb_ptr->curr_pages <
 *              pb_ptr->max_pages.  If it is, return.  Otherwise, continue
 *              the scan until either the above condidtion is fulfilled,
 *              or the head of the LRU is reach.
 *
 *              Under normal circumstances, it should always be possible
 *              to reduce the size of the page buffer below pb_ptr->max_pages.
 *              However, due to prohibition on evicting entries on the 
 *              tick list, and either flushing or evicting entries on the
 *              delayed write list, this will not in general be the case
 *              if pb_ptr->vfd_swmr_writer is TRUE.  In this case, the 
 *              page buffer may exceed its maximum size by an arbitrary 
 *              amount.
 *
 *              If this situation occurs with any regularity, we will 
 *              need a mechanism to avoid attempts to make space when 
 *              it is not possible to do so.
 *
 * Return:	SUCCEED if no errors are encountered, and 
 *              FAIL otherwise.
 *
 * Programmer:	John Mainzer -- 10/14/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__make_space(H5F_t *f, H5PB_t *pb_ptr, H5FD_mem_t inserted_type)
{
    hbool_t inserting_md;
    H5PB_entry_t *search_ptr;
    H5PB_entry_t *flush_ptr;
    H5PB_entry_t *evict_ptr;
    herr_t ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* sanity checks */
    HDassert(f);
    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(pb_ptr->min_md_pages + pb_ptr->min_rd_pages <= pb_ptr->max_pages);

    inserting_md = ( H5FD_MEM_DRAW != inserted_type );

    if ( ( inserting_md ) && ( pb_ptr->min_rd_pages == pb_ptr->max_pages ) )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, 
            "can't make space for metadata -- pb config for raw data only")

    if ( ( ! inserting_md ) && ( pb_ptr->min_md_pages == pb_ptr->max_pages ) )

        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, 
            "can't make space for raw data -- pb config for metadata only")

    search_ptr = pb_ptr->LRU_tail_ptr;

    while ( ( search_ptr ) && ( pb_ptr->curr_pages >= pb_ptr->max_pages ) ) { 

        HDassert(search_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);

        if ( search_ptr->modified_this_tick ) { /* entry is on tick list */

            search_ptr = search_ptr->prev;
            H5PB__UPDATE_STATS_FOR_LRU_TL_SKIP(pb_ptr);

        } else if ( ( inserting_md ) &&
                    ( ! (search_ptr->is_metadata) ) &&
                    ( pb_ptr->curr_rd_pages <= pb_ptr->min_rd_pages ) ) {

            search_ptr = search_ptr->prev;
            H5PB__UPDATE_STATS_FOR_LRU_RD_SKIP(pb_ptr);

        } else if ( ( ! inserting_md ) &&
                    ( search_ptr->is_metadata ) &&
                    ( pb_ptr->curr_md_pages <= pb_ptr->min_md_pages ) ) {

            search_ptr = search_ptr->prev;
            H5PB__UPDATE_STATS_FOR_LRU_MD_SKIP(pb_ptr);

        } else if ( search_ptr->is_dirty ) {

            /* One can make the argument that we should test for dirty 
             * entries first, instead of skipping potentially dirty 
             * entries in the above clauses.  However, I suspect that 
             * this would result in excessive flushes.  Lets try it 
             * this way for now.
             */

            flush_ptr = search_ptr;

            /* if the *search_ptr has a predecessor in the LRU, 
             * set set search_ptr equal to search_ptr->prev.  Otherwise,
             * leave search_ptr unchanged, so that it can be examined 
             * on the next pass through the while loop after it has been
             * flushed.
             */
            if ( search_ptr->prev ) {

                search_ptr = search_ptr->prev;
            }

            if ( H5PB__flush_entry(f, pb_ptr, flush_ptr) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                            "Can't flush entry")

        } else { /* evict the entry */

            evict_ptr = search_ptr;
            search_ptr = search_ptr->prev;
            if ( H5PB__evict_entry(pb_ptr, evict_ptr, FALSE) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                            "Can't evict entry")
        }
    }

    HDassert( ( search_ptr == NULL ) || 
              ( pb_ptr->curr_pages < pb_ptr->max_pages ) );

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB__make_space() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__mark_entry_clean
 *
 * Purpose:	Mark the target entry clean
 *
 *              This function is typically used when an entry has been
 *              completely overwritten and is about to be evicted.  In
 *              this case, the entry must be marked clean to avoid 
 *              sanity check failures on evictions.
 *
 *              While this function does update the index for the 
 *              entry clean, it does not update the replacement policy.
 *              If this is desired, it must be done by the caller.   
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/14/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__mark_entry_clean(H5PB_t *pb_ptr, H5PB_entry_t *entry_ptr)
{
    herr_t ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* sanity checks */
    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(entry_ptr);
    HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
    HDassert(entry_ptr->size > 0);
    HDassert(entry_ptr->size >= pb_ptr->page_size);
    HDassert((entry_ptr->size == pb_ptr->page_size) || (entry_ptr->is_mpmde));
    HDassert(entry_ptr->image_ptr);
    HDassert((pb_ptr->vfd_swmr_writer) || (!(entry_ptr->is_mpmde)));

    /* mark the entry clean */
    entry_ptr->is_dirty = FALSE;

    /* update the index for the entry clean */
    H5PB__UPDATE_INDEX_FOR_ENTRY_CLEAN(pb_ptr, entry_ptr)

    /* don't update the replacement policy -- this will be done by 
     * the caller if desired.
     */

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB__mark_entry_clean() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__mark_entry_dirty
 *
 * Purpose:	Mark the target entry as dirty.
 *
 *              If pb_ptr->vfd_swmr_writer is FALSE, the entry will be 
 *              in the replacement policy.  In this, we simply mark the 
 *              entry as dirty, and update the replacement policy for an 
 *              access.
 *
 *              If pb_ptr->vfd_swmr_writer, it is possible that we must 
 *              delay writes to the target page or multi-page metadata 
 *              entry to avoid message from the future bugs on the VFD 
 *              SWMR readers.  In such cases we must set the 
 *              delay_write_until field and insert the entry on the 
 *              delayed write list instead of the replacement policy.
 *              
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/14/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__mark_entry_dirty(H5F_t * f, H5PB_t *pb_ptr, H5PB_entry_t *entry_ptr)
{
    herr_t ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* sanity checks */
    HDassert(pb_ptr);
    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(entry_ptr);
    HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
    HDassert(entry_ptr->size > 0);
    HDassert(entry_ptr->size >= pb_ptr->page_size);
    HDassert((entry_ptr->size == pb_ptr->page_size) || (entry_ptr->is_mpmde));
    HDassert(entry_ptr->image_ptr);
    HDassert((pb_ptr->vfd_swmr_writer) || (!(entry_ptr->is_mpmde)));

    /* mark the entry dirty if necessary */
    if ( ! ( entry_ptr->is_dirty ) ) {

        entry_ptr->is_dirty = TRUE;

        H5PB__UPDATE_INDEX_FOR_ENTRY_DIRTY(pb_ptr, entry_ptr)

        /* since the entry was clean, there can be no pending delayed write */
        HDassert(entry_ptr->delay_write_until == 0);

        if ( ( pb_ptr->vfd_swmr_writer ) &&
             ( entry_ptr->loaded ) &&
             ( entry_ptr->mem_type != H5FD_MEM_DRAW ) &&
             ( H5F_vfd_swmr_writer__delay_write(f, entry_ptr->page, 
                                        &(entry_ptr->delay_write_until)) < 0 ) )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                        "get delayed write request failed")

        if ( entry_ptr->delay_write_until > 0 ) {

            if ( ! ( entry_ptr->is_mpmde ) ) { 

                /* remove the entry from the replacement policy */

                H5PB__UPDATE_RP_FOR_REMOVE(pb_ptr, entry_ptr, FAIL)
            }

            H5PB__INSERT_IN_DWL(pb_ptr, entry_ptr, FAIL)

        } else if ( ! (entry_ptr->is_mpmde) ) {

           H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)        

        } else {

            /* the entry should be a multi-page metadata entry that 
             * has been modified this tick.  Thus no action is required.
             */
            HDassert(entry_ptr->is_mpmde);
            HDassert(pb_ptr->vfd_swmr_writer);
        }
    } else if ( ( ! (entry_ptr->is_mpmde) ) && 
                ( entry_ptr->delay_write_until == 0 ) ) {

        /* the entry is dirty and on the replacement policy -- just update
         * the replacement policy for an access 
         */
        H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)        
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5PB__mark_entry_dirty() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__read_meta
 *
 * Purpose:	Satisfy a metadata read in cases 7, 8, 9, and 10) 
 *              H5PB_read().  Specifically:
 *
 *              6) If the read is for metadata and not page aligned, clip
 *                 the read to the end of the current page if necessary.
 *                 Load the relevant page if necessary and satisfy the 
 *                 read from the page buffer.  Note that it there is an
 *                 existing page, it must not be a multi-page metadata 
 *                 entry.  It it is, flag an error.
 *
 *              7) If the read is for metadata, is page aligned, is larger 
 *                 than one page, and there is no entry in the page buffer,
 *                 satisfy the read from the file
 *
 *              8) If the read is for metadata, is page aligned, is larger 
 *                 than one page, and there is a regular entry at the target
 *                 page address, test to see if the last read was for the 
 *                 same address.
 *
 *                 If was, evict the page, and satisfy the read from file.
 *                 Flag an error if the page was dirty.
 *
 *                 If the last read was for a different page, clip the read 
 *                 to one page, and satisfy the read from the existing 
 *                 regular entry.
 *
 *              9) If the read is for metadata, is page aligned, is larger
 *                 than one page, and there is a multi-page metadata entry
 *                 at the target page address, test to see if 
 *                 pb_ptr->vfd_swmr_write is TRUE.
 *
 *                 If it is, satisfy the read from the multi-page metadata
 *                 entry, clipping the read if necessary.
 *
 *                 if pb_ptr->vfd_swmr_write is FALSE, flag an error.
 *
 *             10) If the read is for metadata, is page aligned, is no 
 *                 larger than a page, test to see if the page buffer 
 *                 contains a page at the target address.
 *
 *                 If it doesn't, load the page and satisfy the read 
 *                 from it.
 *
 *                 If it contains a regular page entry, satisfy the read 
 *                 from it.
 *
 *                 If it contains a multipage metadata entry at the target
 *                 address, satisfy the read from the multi-page metadata
 *                 entry if pb_ptr->vfd_swmr_write is TRUE, and flag an 
 *                 error otherwise.
 *
 *              The above case analysis may be a bit hard to read.  If so,
 *              the table shown below may help to clarify.  Here:
 *
 *                P/A       == page aligned
 *                size > PL == size > page length
 *                PA        == previous address
 *                A         == current address
 *
 *              In the entry exists column:
 *
 *                N         == no entry
 *                R         == regular (1 page) entry
 *                MPMDE     == multi-page metadata entry
 *
 *       | size | entry  | VFD  |         |
 *  P/A: | > PL | exists | SWMR | PA == A | Comments:
 * ------+------+--------+------+---------+-------------------------------------
 *   N   |  X   | N || R |  X   |    X    | Clip read to page boundary if 
 *       |      |        |      |         | necessary
 *       |      |        |      |         | Load entry if necessary
 *       |      |        |      |         | Satisfy read from entry (case 6)
 * ------+------+--------+------+---------+-------------------------------------
 *   N   |  X   | MPMDE  |  X   |    X    | Error (case 6)
 * ------+------+--------+------+---------+-------------------------------------
 *       |      |        |      |         |
 * ------+------+--------+------+---------+-------------------------------------
 *   Y   |  Y   |   N    |  X   |    X    | Satisfy read from file (case 7)
 * ------+------+--------+------+---------+-------------------------------------
 *   Y   |  Y   |   R    |  X   |    N    | Clip read to page boundary
 *       |      |        |      |         | Satisfy read from entry  (case 8)
 * ------+------+--------+------+---------+-------------------------------------
 *   Y   |  Y   |   R    |  X   |    Y    | Evict entry 
 *       |      |        |      |         | (must be clean -- flag error if not)
 *       |      |        |      |         | Satisfy read from file (case 8)
 * ------+------+--------+------+---------+-------------------------------------
 *   Y   |  Y   | MPMDE  |  N   |    X    | Error (case 9)
 * ------+------+--------+------+---------+-------------------------------------
 *   Y   |  Y   | MPMDE  |  Y   |    X    | Clip read to MPE size if required.
 *       |      |        |      |         | Satify read from MPE (case 9)
 * ------+------+--------+------+---------+-------------------------------------
 *       |      |        |      |         |
 * ------+------+--------+------+---------+-------------------------------------
 *   Y   |  N   |   N    |  X   |    X    | Load entry
 *       |      |        |      |         | Satisfy read from entry (case 10)
 * ------+------+--------+------+---------+-------------------------------------
 *   Y   |  N   |   R    |  X   |    X    | Satisfy read from entry (case 10)
 * ------+------+--------+------+---------+-------------------------------------
 *   Y   |  N   | MPMDE  |  Y   |    X    | Satisfy read from entry (case 10)
 * ------+------+--------+------+---------+-------------------------------------
 *   Y   |  N   | MPMDE  |  N   |    X    | Error (case 10)
 * ------+------+--------+------+---------+-------------------------------------
 *                 
 *              Observe that the above cases imply that:
 *
 *              1) The page buffer is defined.
 *
 *              2) The page buffer has been configured to accept at least
 *                 one page of metadata.
 *
 *              3) This is a metadata read.
 *
 *              Note also that if the metadata read is of size 
 *              no larger than page size, it may not cross page 
 *              boundaries.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/11/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__read_meta(H5F_t *f, H5FD_mem_t type, haddr_t addr, size_t size, 
                void *buf/*out*/)
{
    H5PB_t *pb_ptr;                         /* Page buffer for this file */
    H5PB_entry_t *entry_ptr;                /* Pointer to page buffer entry */
#if VFD_IO /* JRM */
    H5FD_t *file;                           /* File driver pointer */
#endif /* VFD_IO */ /* JRM */
    uint64_t page;		            /* page offset of addr */
    haddr_t page_addr;                      /* page containg addr */
    static haddr_t prev_addr = HADDR_UNDEF; /* addr of last call */
    size_t offset;                          /* offset of read in page */
    size_t clipped_size;                    /* possibley clipped size */
    herr_t ret_value = SUCCEED;             /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->pb_ptr);

    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(pb_ptr->min_rd_pages < pb_ptr->max_pages);
    HDassert(f->shared->lf);

#if VFD_IO /* JRM */
    file = f->shared->lf;
#endif /* VFD_IO */ /* JRM */

    HDassert(H5FD_MEM_DRAW != type);
    HDassert(buf);

    /* Calculate the aligned address of the first page */
    page = (addr / pb_ptr->page_size);
    page_addr = page * pb_ptr->page_size;

    if ( page_addr != addr ) { /* case 6 */
 
        /* If the read is for metadata and not page aligned, clip
         * the read to the end of the current page if necessary.
         * Load the relevant page if necessary and satisfy the 
         * read from the page buffer.  Note that it there is an
         * existing page, it must not be a multi-page metadata 
         * entry.  It it is, flag an error.
         */

        offset = addr - page_addr;

        if ( (offset + size) <= pb_ptr->page_size ) {

            clipped_size = size;

        } else {

            clipped_size = size - ( (offset + size) - pb_ptr->page_size);
        }

        HDassert( clipped_size > 0 );
        HDassert( clipped_size <= size );
        HDassert( (offset + clipped_size) <= pb_ptr->page_size );

        /* get the containing page */
        H5PB__SEARCH_INDEX(pb_ptr, page, entry_ptr, FAIL)

        /* update hit rate stats */
        H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, ((entry_ptr) != NULL), \
                                       TRUE, FALSE)

        if ( ( NULL == entry_ptr ) &&
             ( H5PB__load_page(f, pb_ptr, page_addr, type, &entry_ptr) < 0 ) )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                        "page buffer page load request failed (1)")

        HDassert(entry_ptr);
        HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
        HDassert(entry_ptr->addr == page_addr);
        HDassert(entry_ptr->is_metadata);
        HDassert(!(entry_ptr->is_mpmde));

        /* copy data from the page into read buffer */
        HDmemcpy((uint8_t *)buf, (uint8_t *)(entry_ptr->image_ptr) + offset, 
                 clipped_size);

        /* if the entry is on the LRU, update the replacement policy */
        if ( ( ! (entry_ptr->is_mpmde) ) && 
             ( entry_ptr->delay_write_until == 0 ) ) {

           H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)        
        }
    } else {

        HDassert( page_addr == addr );

        if ( size >= pb_ptr->page_size ) {

            /* search the page buffer for an entry at page */
            H5PB__SEARCH_INDEX(pb_ptr, page, entry_ptr, FAIL)


            if ( entry_ptr == NULL ) { /* case 7 */

                /* update hit rate stats */
                H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, FALSE, TRUE, size > pb_ptr->page_size)

                /* If the read is for metadata, is page aligned, is larger 
                 * than one page, and there is no entry in the page buffer,
                 * satisfy the read from the file
                 */
#if VFD_IO /* JRM */
                if ( H5FD_read(file, type, addr, size, buf) < 0)
#else /* VFD_IO */ /* JRM */
                if ( H5F__accum_read(f, type, addr, size, buf) < 0 )
#endif /* VFD_IO */ /* JRM */

                    HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                                "driver read request failed (1)")

                H5PB__UPDATE_STATS_FOR_BYPASS(pb_ptr, type, size);
            } else {

                HDassert( entry_ptr );
                HDassert( entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC );
                HDassert( entry_ptr->is_metadata );

                if ( ! ( entry_ptr->is_mpmde ) ) { /* case 8 */

                    /* If the read is for metadata, is page aligned, is larger 
                     * than one page, and there is a regular entry at the target
                     * page address, test to see if the last read was for the 
                     * same address.
                     *
                     * If was, evict the page, and satisfy the read from file.
                     * Flag an error if the page was dirty.
                     *
                     * If the last read was for a different page, clip the read 
                     * to one page, and satisfy the read from the existing 
                     * regular entry.
                     */

                    HDassert( entry_ptr->size == pb_ptr->page_size );

                    if ( addr == prev_addr ) {

                        /* since this is a second try, don't update 
                         * hit rate stats.
                         */

                        HDassert( ! ( entry_ptr->is_dirty ) );

                        if ( H5PB__evict_entry(pb_ptr, entry_ptr, TRUE) < 0 )

                            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                                        "forced eviction failed (1)")
#if VFD_IO  /* JRM */
                        if ( H5FD_read(file, type, addr, size, buf) < 0)
#else /* VFD_IO */ /* JRM */
                        if ( H5F__accum_read(f, type, addr, size, buf) < 0 )
#endif /* VFD_IO */ /* JRM */

                            HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                                        "driver read request failed (2)")

                        H5PB__UPDATE_STATS_FOR_BYPASS(pb_ptr, type, size);
                    } else {

                        HDassert( entry_ptr->image_ptr );

                        /* copy data from the page into read buffer */
                        HDmemcpy((uint8_t *)buf, 
                                 (uint8_t *)(entry_ptr->image_ptr), 
                                 entry_ptr->size);

                        /* if the entry is on the LRU, update the replacement 
                         * policy 
                         */
                        if ( ( ! (entry_ptr->is_mpmde) ) && 
                             ( entry_ptr->delay_write_until == 0 ) ) {

                           H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)
                        }

                        /* update hit rate stats */
                        H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, TRUE, TRUE, FALSE)
                    }
                } else { /* case 9 */

                    /* If the read is for metadata, is page aligned, is larger
                     * than one page, and there is a multi-page metadata entry
                     * at the target page address, test to see if 
                     * pb_ptr->vfd_swmr_write is TRUE.
                     *
                     * If it is, satisfy the read from the multi-page metadata
                     * entry, clipping the read if necessary.
                     *
                     * if pb_ptr->vfd_swmr_write is FALSE, flag an error.
                     */
                    HDassert( entry_ptr->is_mpmde );
                    HDassert( pb_ptr->vfd_swmr_writer );

                    if ( size > entry_ptr->size ) {

                        clipped_size = entry_ptr->size;

                    } else {

                        clipped_size = size;
                    }
                    
                    /* copy data from the page into read buffer */
                    HDmemcpy((uint8_t *)buf, (uint8_t *)(entry_ptr->image_ptr), 
                             clipped_size);

                    /* if the entry is on the LRU, update the replacement 
                     * policy 
                     */
                    if ( ( ! (entry_ptr->is_mpmde) ) && 
                         ( entry_ptr->delay_write_until == 0 ) ) {

                       H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)
                    }

                    /* update hit rate stats */
                    H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, TRUE, TRUE, TRUE)
                }
            }
        } else { /* case 10 */
 
            /* If the read is for metadata, is page aligned, is no 
             * larger than a page, test to see if the page buffer 
             * contains a page at the target address.
             *
             * If it doesn't, load the page and satisfy the read 
             * from it.
             *
             * If it contains a regular page entry, satisfy the read 
             * from it.
             *
             * If it contains a multipage metadata entry at the target
             * address, satisfy the read from the multi-page metadata
             * entry if pb_ptr->vfd_swmr_write is TRUE, and flag an 
             * error otherwise.
             */
            HDassert( size <= pb_ptr->page_size );

            /* get the containing page */
            H5PB__SEARCH_INDEX(pb_ptr, page, entry_ptr, FAIL)

            /* update hit rate stats */
            H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, (entry_ptr != NULL), \
                                           TRUE, FALSE)

            if ( ( NULL == entry_ptr ) &&
                 ( H5PB__load_page(f, pb_ptr, page_addr, type, &entry_ptr) < 0))

                HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                            "page buffer page load request failed (2)")

            HDassert( entry_ptr );
            HDassert( entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC );
            HDassert( entry_ptr->is_metadata );
            HDassert( ( ! ( entry_ptr->is_mpmde ) ) ||
                      ( pb_ptr->vfd_swmr_writer) );

            /* copy data from the page into read buffer */
            HDmemcpy((uint8_t *)buf, (uint8_t *)(entry_ptr->image_ptr), size);

            /* if the entry is on the LRU, update the replacement policy */
            if ( ( ! (entry_ptr->is_mpmde) ) && 
                 ( entry_ptr->delay_write_until == 0 ) ) {

               H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)
            }
        }
    }

    prev_addr = addr;

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* end H5PB__read_meta() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__read_raw
 *
 * Purpose:	Satisfy a raw data read in cases 3 and 4 from H5PB_read().
 *              Specifically:
 *
 *              3) If the read is for raw data, and it is larger than the 
 *                 page size, read it directly from the HDF5 file.  
 *
 *                 It is possible that the page buffer contains dirty pages 
 *                 that intersect with the read -- test for this and update
 *                 the read buffer from the page buffer if any such pages 
 *                 exist. 
 *
 *                 Note that no pages are inserted into the page buffer in 
 *                 this case.
 *
 *              4) If the read is for raw data, and it is of size less 
 *                 than or equal to the page size, satisfy the read from 
 *                 the page buffer, loading and inserting pages into the 
 *                 page buffer as necessary
 *
 *              Observe that this implies that:
 *
 *              1) The page buffer is defined.
 *
 *              2) The page buffer has been configured to accept at least
 *                 one page of raw data.
 *
 *              2) This is a raw data read.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/11/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__read_raw(H5F_t *f, H5FD_mem_t type, haddr_t addr, size_t size, 
               void *buf/*out*/)
{
    H5PB_t *pb_ptr;                    /* Page buffer for this file */
    H5PB_entry_t *entry_ptr;           /* Pointer to page buffer entry */
    uint64_t first_page;		/* page offset of first I/O */
    uint64_t last_page;                 /* page offset of last I/O */
    uint64_t search_page;               /* page offset of current page */
    haddr_t first_page_addr;            /* address of first page of I/O */
    haddr_t last_page_addr;             /* address of last page of I/O */
    haddr_t search_addr;                /* Address of current page */
    hsize_t num_touched_pages;          /* Number of pages accessed */
    size_t offset;                      /* offset of read in page */
    size_t length;                      /* length of read in page */
    hsize_t i;                          /* Local index variable */
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->pb_ptr);

    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(pb_ptr->min_md_pages < pb_ptr->max_pages);
    HDassert(H5FD_MEM_DRAW == type);


    /* Calculate the aligned address of the first page */
    first_page = (addr / pb_ptr->page_size);
    first_page_addr = first_page * pb_ptr->page_size;

    /* Calculate the aligned address of the last page */
    last_page = ((addr + size - 1) / pb_ptr->page_size);
    last_page_addr = last_page * pb_ptr->page_size;

    /* Calculate number of pages that this read spans. */
    num_touched_pages = last_page - first_page + 1;

    if ( first_page_addr == last_page_addr ) {

        HDassert(1 == num_touched_pages);
        last_page_addr = HADDR_UNDEF;

    }

    /* case 3) raw data read of page size or greater. */
    if ( size >= pb_ptr->page_size ) {

#if VFD_IO
        if ( H5FD_read(f->shared->lf, type, addr, size, buf) < 0)
#else /* VFD_IO */
        if ( H5F__accum_read(f, type, addr, size, buf) < 0 )
#endif /* VFD_IO */

            HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                        "read through metadata accumulator failed")


        H5PB__UPDATE_STATS_FOR_BYPASS(pb_ptr, type, size);


        /* For each page that intersects with the above read, check to see 
         * if it exists in the page buffer, and if so, if it is dirty.
         *
         * If it does and is, update the read buffer with the contents 
         * of the page so we get the up to date data into the buffer 
         * after the big read from the file.
         */
        search_page = first_page;
        search_addr = first_page_addr;

        for(i = 0; i < num_touched_pages; i++) {

            H5PB__SEARCH_INDEX(pb_ptr, search_page, entry_ptr, FAIL)

            /* update hit rate stats */
            H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, (entry_ptr != NULL), \
                                           FALSE, FALSE)

            if ( entry_ptr ) {

                HDassert( entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC );
                HDassert( ! ( entry_ptr->is_metadata ) );
                HDassert( entry_ptr->page == search_page );
                HDassert( entry_ptr->addr == search_addr );
                HDassert( entry_ptr->size == pb_ptr->page_size );
                HDassert( entry_ptr->delay_write_until == 0 );
                HDassert( entry_ptr->addr <= addr + size );
                HDassert( entry_ptr->addr + entry_ptr->size <= addr + size );

                if ( entry_ptr->is_dirty ) {

                    if ( i == 0 ) {

                        /* handle the possible partial access of the 
                         * first page.
                         */

                        HDassert( search_addr == first_page_addr );
                        HDassert( search_page == first_page );

                        offset = addr - first_page_addr;

                        HDassert((( offset == 0 ) && (search_addr == addr )) ||
                                 (( offset > 0 ) && ( search_addr < addr )));

                        HDassert(pb_ptr->page_size >= offset);

                        HDassert( size >=  pb_ptr->page_size - (size_t)offset );

                        HDmemcpy(buf, (uint8_t *)entry_ptr->image_ptr + offset, 
                                 pb_ptr->page_size - (size_t)offset);

                    } else if ( i == num_touched_pages - 1 ) {

                        /* handle the possible partial access of the 
                         * last page.
                         */
                        HDassert( i > 0 );
                        HDassert( search_addr == last_page_addr );
                        HDassert( search_page == last_page );
                        HDassert( addr < last_page_addr );
                        HDassert( last_page_addr < addr + size ); 

                        offset = (num_touched_pages - 2) * pb_ptr->page_size + 
                                 (pb_ptr->page_size - (addr - first_page_addr));

                        HDmemcpy((uint8_t *)buf + offset, entry_ptr->image_ptr,
                                 (size_t)((addr + size) - last_page_addr));

                    } else {

                        /* this is an internal page -- copy it in its 
                         * entireity.
                         */
                    
                        offset = (i - 1) * pb_ptr->page_size + 
                                 (pb_ptr->page_size - (addr - first_page_addr));

                        HDassert ( addr + offset == search_addr );
                        HDassert ( offset + pb_ptr->page_size <= size );

                        HDmemcpy(((uint8_t *)(buf) + offset), 
                                 entry_ptr->image_ptr, 
                                 pb_ptr->page_size);
                    }

                    /* we have touched the entry -- move it to the top
                     * of the LRU if it resides there.
                     *
                     * The entry will be on the LRU if both it is not 
                     * a multi-page metadata entry and it is not 
                     * subject to a delayed write.
                     *
                     * As this is a raw data page buffer entry, both of 
                     * these must be true, and are asserted above.
                     *
                     * Thus, just update the LRU.
                     */
                    H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)

                } /* if ( entry_ptr->is_dirty ) */
            } /* if ( entry_ptr ) */

            search_page++;
            search_addr += pb_ptr->page_size;

        } /* end for */
    } else {
        /* case 4: Raw data read of size less than page size. 
         *
         * In this case, read the desired data from the page buffer, loading
         * pages if necessary.
         */
        HDassert(size < pb_ptr->page_size);

        /* first page */
        offset = addr - first_page_addr;

        if ( (offset + size) <= pb_ptr->page_size ) {

            HDassert(num_touched_pages == 1);
            length = size;

        } else {

            HDassert(num_touched_pages == 2);
            length = size - (pb_ptr->page_size - offset);
        }

        /* get the first page */
        H5PB__SEARCH_INDEX(pb_ptr, first_page, entry_ptr, FAIL)

        /* update hit rate stats */
        H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, (entry_ptr != NULL), \
                                       FALSE, FALSE)

        if ( ( NULL == entry_ptr ) &&
             ( H5PB__load_page(f, pb_ptr, first_page_addr, 
                                type, &entry_ptr) < 0 ) )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                        "page buffer page load request failed (1)")

        HDassert(entry_ptr);
        HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
        HDassert(entry_ptr->addr == first_page_addr);


        /* copy data from first page into read buffer */
        HDmemcpy((uint8_t *)buf, ((uint8_t *)(entry_ptr->image_ptr) + offset), 
                 length);

        H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)

        /* second page, if it exists */
        if ( num_touched_pages == 2 ) {

            offset = length;
            length = size - offset;

            HDassert(offset + length == size);

            /* get the second page */
            H5PB__SEARCH_INDEX(pb_ptr, last_page, entry_ptr, FAIL)

            /* update hit rate stats */
            H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, (entry_ptr != NULL), \
                                           FALSE, FALSE)

            if ( ( NULL == entry_ptr ) &&
                 ( H5PB__load_page(f, pb_ptr, last_page_addr, 
                                    type, &entry_ptr) < 0 ) )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                            "page buffer page load request failed (2)")

            HDassert(entry_ptr);
            HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
            HDassert(entry_ptr->addr == last_page_addr);
            HDassert(entry_ptr->page == last_page);

            /* copy data from second page into read buffer */
            HDmemcpy(((uint8_t *)(buf) + offset), 
                     (uint8_t *)(entry_ptr->image_ptr), length);
        
            H5PB__UPDATE_RP_FOR_ACCESS(pb_ptr, entry_ptr, FAIL)
        }
    } /* end else */

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* end H5PB__read_raw() */


/*-------------------------------------------------------------------------
 *
 * Function:	H5PB__write_meta
 *
 * Purpose:	Satisfy a metadata read in cases 7 and 8 from H5PB_write().
 *              Specifically:
 *
 *              7) If the write is of metadata, the write is larger than
 *                 one page, and vfd_swmr_writer is TRUE, the write must
 *                 buffered in the page buffer until the end of the tick.
 *
 *                 If it doesn't exist already, create a multi-page metadata 
 *                 entry in the page buffer and copy the write into it.  
 *                 Insert the new entry in the tick list if necessary.
 *
 *                 Test to see if the write of the multi-page metadata 
 *                 entry must be delayed.  If so, place the entry in 
 *                 the delayed write list.  Otherwise, the multi-page
 *                 metadata entry will be written to the HDF5 file and
 *                 evicted when the tick list is released at the of the 
 *                 tick.
 *
 *              8) If the write is of metadata, and the write is of size
 *                 less than or equal to the page size, write the data
 *                 into the page buffer, loading and inserting a page 
 *                 if necessary.
 *
 *                 If, in addition, vfd_swmr_writer is TRUE, we must:
 *
 *                  * add the page touched by the write to the tick list
 *                    so that it will be buffered until the end of the 
 *                    tick.
 *
 *                  * test to see if the write must be delayed, and 
 *                    add the page to the delayed write list if so.
 *
 *              Observe that this implies that:
 *
 *              1) The page buffer is defined.
 *
 *              2) The page buffer has been configured to accept at least
 *                 one page of metadata.
 *
 *              3) This is a metadata read.
 *
 *              Note also that if the metadata read is of size 
 *              no larger than page size, it may not cross page 
 *              boundaries.
 *
 *              Further, for reads larger than page size (case 7 only), 
 *              the base address must be page aligned.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/11/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__write_meta(H5F_t *f, H5FD_mem_t type, haddr_t addr, size_t size, 
                 const void *buf/*out*/)
{
    H5PB_t *pb_ptr;                    /* Page buffer for this file */
    H5PB_entry_t *entry_ptr;           /* Pointer to page buffer entry */
    uint64_t page;		        /* page offset of addr */
    haddr_t page_addr;                  /* page containg addr */
    size_t offset;                      /* offset of write in page */
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->pb_ptr);

    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(pb_ptr->min_rd_pages < pb_ptr->max_pages);
    HDassert(H5FD_MEM_DRAW != type);
    HDassert(buf);

    /* Calculate the aligned address of the first page */
    page = (addr / pb_ptr->page_size);
    page_addr = page * pb_ptr->page_size;

    /* if size > pb_ptr->page_size, addr must be page aligned */
    HDassert((size <= pb_ptr->page_size) || (addr == page_addr));


    /* case 7) metadata write of size greater than page size. */
    if ( size > pb_ptr->page_size ) {

        /* The write must be for a multi-page metadata entry, and 
         * we must be running as a VFD SWMR writer.
         *
         * This requires the following actions:
         *
         * 1) If the multi-page metadata entry is not alrady in the 
         *    page buffer, create an entry for it.
         *
         * 2) Overwrite the image of the entry with the write buffer.
         *
         * 3) If the entry is not alread on the tick list, add it to 
         *    the tick list.
         * 
         * 4) If the entry is not alread on the delayed write list,
         *    test to see if it should be, and move it from the 
         *    LRU to the delayed write list and set the delay_write_until
         *    field appropriately.
         *
         *    This is done via the call to H5PB__mark_entry_dirty()
         */
        HDassert(pb_ptr->vfd_swmr_writer);
        HDassert(addr == page_addr);

        H5PB__SEARCH_INDEX(pb_ptr, page, entry_ptr, FAIL)

        /* update hit rate stats */
        H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, (entry_ptr != NULL), \
                                      TRUE, TRUE)

        if ( NULL == entry_ptr ) {

            /* the multi-page metadata entry is not currently in the page 
             * buffer.  Create an entry for it, and insert it into the LRU.
             *
             * Don't bother to try to make space for it, as VFD SWMR 
             * ignores the limits on page buffer size.
             */
            if ( H5PB__create_new_page(pb_ptr, addr, size, type, 
                                       FALSE, &entry_ptr) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                            "can't create new page buffer page")

            /* set entry_ptr->loaded to TRUE so as to trigger the 
             * the delayed write test in H5PB__mark_entry_dirty().
             */
            entry_ptr->loaded = TRUE;
        }

        /* at this point, one way or the other, the multi-page metadata 
         * entry must be in the page buffer.
         */
        HDassert(entry_ptr->is_metadata);
        HDassert(entry_ptr->is_mpmde);
        HDassert(size == entry_ptr->size);
        HDassert(type == entry_ptr->mem_type);

        /* overwrite the entry image with the write buffer */
        HDmemcpy((uint8_t *)(entry_ptr->image_ptr), buf, size);

        /* mark the entry dirty */
        if ( H5PB__mark_entry_dirty(f, pb_ptr, entry_ptr) < 0 )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                        "mark entry dirty failed (1)")

        /* insert in tick list if not there already */
        if ( ! ( entry_ptr->modified_this_tick ) ) {

            entry_ptr->modified_this_tick = TRUE;

            H5PB__INSERT_IN_TL(pb_ptr, entry_ptr, FAIL)
        }


    } else {
        /* case 8) metadata write of size no larger than page size */

        offset = addr - page_addr;

        /* write cannot cross page boundaries. */
        HDassert((offset + size) <= pb_ptr->page_size);

        /* get the containing page */
        H5PB__SEARCH_INDEX(pb_ptr, page, entry_ptr, FAIL)

        /* update hit rate stats */
        H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, (entry_ptr != NULL), \
                                      TRUE, FALSE)

        if ( ( NULL == entry_ptr ) &&
             ( H5PB__load_page(f, pb_ptr, page_addr, type, &entry_ptr) < 0 ) )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                        "page buffer page load request failed (1)")

        HDassert(entry_ptr);
        HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
        HDassert(entry_ptr->addr == page_addr);
        HDassert(entry_ptr->is_metadata);
        HDassert(!(entry_ptr->is_mpmde));
        HDassert(entry_ptr->size == pb_ptr->page_size);
        HDassert(size <= entry_ptr->size);

        /* copy data from the write buffer into the page image */
        HDmemcpy(((uint8_t *)(entry_ptr->image_ptr) + offset), 
                 (const uint8_t *)buf, size);

        if ( H5PB__mark_entry_dirty(f, pb_ptr, entry_ptr) < 0 )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                        "mark entry dirty failed (2)")

        if ( pb_ptr->vfd_swmr_writer ) {

            /* test to see if the entry is on the tick list, and insert 
             * it if it is not. This will force the page buffer to retain 
             * the page until the end of the tick.
             */
            if ( ! ( entry_ptr->modified_this_tick ) ) {

                entry_ptr->modified_this_tick = TRUE;

                H5PB__INSERT_IN_TL(pb_ptr, entry_ptr, FAIL)
            }
        }
    } 

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* end H5PB__write_meta() */


/*-------------------------------------------------------------------------
 *
 * Function:    H5PB__write_raw
 *
 * Purpose:     Satisfy a raw data write in cases 3 and 4 from H5PB_write().
 *              Specifically:
 *
 *              3) If the write is raw data, and it of page size or 
 *                 larger, write directly to the HDF5 file.  
 *
 *                 It is possible that the write intersects one or more 
 *                 pages in the page buffer -- test for this and update
 *                 any partially written pages, and evict any pages 
 *                 that are completely overwritten.
 *
 *                 Note that no pages are inserted into the page buffer in 
 *                 this case.
 *
 *              4) If the write is of raw data, and it is of size less 
 *                 than the page size, write the page into the page
 *                 buffer, loading and inserting pages into the 
 *                 page buffer as necessary
 *
 *              Observe that this implies that:
 *
 *              1) The page buffer is defined.
 *
 *              2) The page buffer has been configured to accept at least
 *                 one page of raw data.
 *
 *              2) This is a raw data write.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer -- 10/11/18
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5PB__write_raw(H5F_t *f, H5FD_mem_t type, haddr_t addr, size_t size, 
                const void *buf/*out*/)
{
    H5PB_t *pb_ptr;                    /* Page buffer for this file */
    H5PB_entry_t *entry_ptr;           /* Pointer to page buffer entry */
    uint64_t first_page;		/* page offset of first I/O */
    uint64_t last_page;                 /* page offset of last I/O */
    uint64_t search_page;               /* page offset of current page */
    haddr_t first_page_addr;            /* address of first page of I/O */
    haddr_t last_page_addr;             /* address of last page of I/O */
    haddr_t search_addr;                /* Address of current page */
    hsize_t num_touched_pages;          /* Number of pages accessed */
    hsize_t i;                          /* Local index variable */
    size_t length;                      /* length of write in a page */
    size_t offset;                      /* offset of write in a page */
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    HDassert(f->shared->pb_ptr);

    pb_ptr = f->shared->pb_ptr;

    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
    HDassert(pb_ptr->min_md_pages < pb_ptr->max_pages);
    HDassert(f->shared->lf);

    HDassert(H5FD_MEM_DRAW == type);

    /* Calculate the aligned address of the first page */
    first_page = (addr / pb_ptr->page_size);
    first_page_addr = first_page * pb_ptr->page_size;

    /* Calculate the aligned address of the last page */
    last_page = ((addr + size - 1) / pb_ptr->page_size);
    last_page_addr = last_page * pb_ptr->page_size;

    /* Calculate number of pages that this read spans. */
    num_touched_pages = last_page - first_page + 1;

    if ( first_page_addr == last_page_addr ) {

        HDassert(1 == num_touched_pages);
        last_page_addr = HADDR_UNDEF;

    }

    /* case 3) raw data write of page size or greater. */
    if ( size >= pb_ptr->page_size ) {
#if VFD_IO
        if ( H5FD_write(f->shared->lf, type, addr, size, buf) < 0 )
#else /* VFD_IO */
        if ( H5F__accum_write(f, type, addr, size, buf) < 0 )
#endif /* VFD_IO */

            HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
                        "write through metadata accumulator failed")


        H5PB__UPDATE_STATS_FOR_BYPASS(pb_ptr, type, size);

        /* For each page that intersects with the above write, check to see 
         * if it exists in the page buffer.
         *
         * If it does and is, and if the write overwrites page fully,
         * mark the page clean and evict it.
         *
         * If the write only partially intersects a page, update the 
         * page and mark it dirty.
         */
        search_page = first_page;
        search_addr = first_page_addr;

        for(i = 0; i < num_touched_pages; i++) {

            H5PB__SEARCH_INDEX(pb_ptr, search_page, entry_ptr, FAIL)

            /* update hit rate stats */
            H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, (entry_ptr != NULL), \
                                           FALSE, FALSE)

            if ( entry_ptr ) {

                HDassert( entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC );
                HDassert( ! ( entry_ptr->is_metadata ) );
                HDassert( entry_ptr->page == search_page );
                HDassert( entry_ptr->addr == search_addr );
                HDassert( entry_ptr->size == pb_ptr->page_size );
                HDassert( entry_ptr->delay_write_until == 0 );
                HDassert( entry_ptr->addr <= addr + size );

                if ( ( addr <= entry_ptr->addr ) &&
                     ( entry_ptr->addr + entry_ptr->size <= addr + size ) ) {

                    /* the page is completely overwritten -- mark it clean
                     * and evict it.
                     */
                    if ( ( entry_ptr->is_dirty ) && 
                         ( H5PB__mark_entry_clean(pb_ptr, entry_ptr) < 0 ) )

                        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                                    "mark entry clean failed")

                    if ( H5PB__evict_entry(pb_ptr, entry_ptr, TRUE) < 0 )

                        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                                    "forced eviction failed (1)")

                } else if ( i == 0 ) {

                    /* handle partial overwrite of the first page.  */

                    HDassert( search_addr == first_page_addr );
                    HDassert( search_page == first_page );
                    HDassert( search_addr < addr );
                    HDassert( entry_ptr->addr + entry_ptr->size <= 
                              addr + size );

                    offset = addr - first_page_addr;

                    HDassert( offset > 0 );
                    HDassert( pb_ptr->page_size >= offset );
                    HDassert( size >=  pb_ptr->page_size - (size_t)offset );

                    HDmemcpy((uint8_t *)entry_ptr->image_ptr + offset, buf, 
                             pb_ptr->page_size - (size_t)offset);

                    if ( H5PB__mark_entry_dirty(f, pb_ptr, entry_ptr) < 0 )

                        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                                    "mark entry dirty failed (1)")

                } else if ( i == num_touched_pages - 1 ) {

                    /* handle partial overwrite of the last page.  */
                    HDassert( i > 0 );
                    HDassert( search_addr == last_page_addr );
                    HDassert( search_page == last_page );
                    HDassert( addr < last_page_addr );
                    HDassert( last_page_addr < addr + size ); 

                    offset = (num_touched_pages - 2) * pb_ptr->page_size + 
                             (pb_ptr->page_size - (addr - first_page_addr));

                    HDmemcpy(entry_ptr->image_ptr, 
                             (const uint8_t *)buf + offset,
                             (size_t)((addr + size) - last_page_addr));

                    if ( H5PB__mark_entry_dirty(f, pb_ptr, entry_ptr) < 0 )

                        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                                    "mark entry dirty failed (2)")
                } else {

                    /* this should be un-reachable */
                    HDassert(FALSE);

                }
            } /* if ( entry_ptr ) */

            search_page++;
            search_addr += pb_ptr->page_size;

        } /* end for */
    } else {
        /* case 4: Raw data write of size less than page size. 
         *
         * In this case, write the data to the page buffer, loading
         * pages if necessary.
         */
        HDassert(size < pb_ptr->page_size);

        /* first page */
        offset = addr - first_page_addr;

        if ( (offset + size) <= pb_ptr->page_size ) {

            HDassert(num_touched_pages == 1);
            length = size;

        } else {

            HDassert(num_touched_pages == 2);
            length = pb_ptr->page_size - offset;
            HDassert( offset + length == pb_ptr->page_size );
        }

        /* get the first page */
        H5PB__SEARCH_INDEX(pb_ptr, first_page, entry_ptr, FAIL)

        /* update hit rate stats */
        H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, (entry_ptr != NULL), \
                                       FALSE, FALSE)

        if ( ( NULL == entry_ptr ) &&
             ( H5PB__load_page(f, pb_ptr, first_page_addr, 
                                type, &entry_ptr) < 0 ) )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                        "page buffer page load request failed (1)")

        HDassert(entry_ptr);
        HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
        HDassert(entry_ptr->addr == first_page_addr);


        /* copy data from the write buffer into the first page */
        HDmemcpy(((uint8_t *)(entry_ptr->image_ptr)) + offset, 
                 (const uint8_t *)buf, length);

        if ( H5PB__mark_entry_dirty(f, pb_ptr, entry_ptr) < 0 )

            HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                        "mark entry dirty failed (3)")

        /* second page, if it exists */
        if ( num_touched_pages == 2 ) {

            offset = length;
            length = size - offset;

            HDassert(offset + length == size);

            /* get the first page */
            H5PB__SEARCH_INDEX(pb_ptr, last_page, entry_ptr, FAIL)

            /* update hit rate stats */
            H5PB__UPDATE_PB_HIT_RATE_STATS(pb_ptr, (entry_ptr != NULL), \
                                           FALSE, FALSE)

            if ( ( NULL == entry_ptr ) &&
                 ( H5PB__load_page(f, pb_ptr, last_page_addr, 
                                    type, &entry_ptr) < 0 ) )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_READERROR, FAIL, \
                            "page buffer page load request failed (2)")

            HDassert(entry_ptr);
            HDassert(entry_ptr->magic == H5PB__H5PB_ENTRY_T_MAGIC);
            HDassert(entry_ptr->addr == last_page_addr);
            HDassert(entry_ptr->page == last_page);

            /* copy data from the write buffer into the first page */
            HDmemcpy((uint8_t *)(entry_ptr->image_ptr), 
                     ((const uint8_t *)(buf) + offset), length);

            if ( H5PB__mark_entry_dirty(f, pb_ptr, entry_ptr) < 0 )

                HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                            "mark entry dirty failed (3)")
        }
    }

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* end H5PB__write_raw() */