Perform delayed coalescing prior to purging.

Rather than purging uncoalesced extents, perform just enough incremental
coalescing to purge only fully coalesced extents.  In the absence of
cached extent reuse, the immediate versus delayed incremental purging
algorithms result in the same purge order.

This resolves #655.

1 files changed, 113 insertions, 38 deletions

diff --git a/src/extent.c b/src/extent.c
index 09990aa..368c974 100644
--- a/src/extent.c
+++ b/src/extent.c
@@ -69,6 +69,9 @@ static size_t	highpages;
  */
 
 static void extent_deregister(tsdn_t *tsdn, extent_t *extent);
+static extent_t *extent_try_coalesce(tsdn_t *tsdn, arena_t *arena,
+    extent_hooks_t **r_extent_hooks, rtree_ctx_t *rtree_ctx, extents_t *extents,
+    extent_t *extent, bool *coalesced);
 static void extent_record(tsdn_t *tsdn, arena_t *arena,
     extent_hooks_t **r_extent_hooks, extents_t *extents, extent_t *extent);
 
@@ -175,7 +178,7 @@ ph_gen(, extent_heap_, extent_heap_t, extent_t, ph_link, extent_snad_comp)
 
 bool
 extents_init(tsdn_t *tsdn, extents_t *extents, extent_state_t state,
-    bool try_coalesce) {
+    bool delay_coalesce) {
 	if (malloc_mutex_init(&extents->mtx, "extents", WITNESS_RANK_EXTENTS)) {
 		return true;
 	}
@@ -185,7 +188,7 @@ extents_init(tsdn_t *tsdn, extents_t *extents, extent_state_t state,
 	extent_list_init(&extents->lru);
 	extents->npages = 0;
 	extents->state = state;
-	extents->try_coalesce = try_coalesce;
+	extents->delay_coalesce = delay_coalesce;
 	return false;
 }
 
@@ -200,7 +203,8 @@ extents_npages_get(extents_t *extents) {
 }
 
 static void
-extents_insert_locked(tsdn_t *tsdn, extents_t *extents, extent_t *extent) {
+extents_insert_locked(tsdn_t *tsdn, extents_t *extents, extent_t *extent,
+    bool preserve_lru) {
 	malloc_mutex_assert_owner(tsdn, &extents->mtx);
 	assert(extent_state_get(extent) == extents->state);
 
@@ -208,13 +212,16 @@ extents_insert_locked(tsdn_t *tsdn, extents_t *extents, extent_t *extent) {
 	size_t psz = extent_size_quantize_floor(size);
 	pszind_t pind = psz2ind(psz);
 	extent_heap_insert(&extents->heaps[pind], extent);
-	extent_list_append(&extents->lru, extent);
+	if (!preserve_lru) {
+		extent_list_append(&extents->lru, extent);
+	}
 	size_t npages = size >> LG_PAGE;
 	atomic_add_zu(&extents->npages, npages);
 }
 
 static void
-extents_remove_locked(tsdn_t *tsdn, extents_t *extents, extent_t *extent) {
+extents_remove_locked(tsdn_t *tsdn, extents_t *extents, extent_t *extent,
+    bool preserve_lru) {
 	malloc_mutex_assert_owner(tsdn, &extents->mtx);
 	assert(extent_state_get(extent) == extents->state);
 
@@ -222,7 +229,9 @@ extents_remove_locked(tsdn_t *tsdn, extents_t *extents, extent_t *extent) {
 	size_t psz = extent_size_quantize_floor(size);
 	pszind_t pind = psz2ind(psz);
 	extent_heap_remove(&extents->heaps[pind], extent);
-	extent_list_remove(&extents->lru, extent);
+	if (!preserve_lru) {
+		extent_list_remove(&extents->lru, extent);
+	}
 	size_t npages = size >> LG_PAGE;
 	assert(atomic_read_zu(&extents->npages) >= npages);
 	atomic_sub_zu(&extents->npages, size >> LG_PAGE);
@@ -249,22 +258,62 @@ extents_first_best_fit_locked(tsdn_t *tsdn, arena_t *arena, extents_t *extents,
 	return NULL;
 }
 
+static bool
+extent_try_delayed_coalesce(tsdn_t *tsdn, arena_t *arena,
+    extent_hooks_t **r_extent_hooks, rtree_ctx_t *rtree_ctx, extents_t *extents,
+    extent_t *extent) {
+	extent_state_set(extent, extent_state_active);
+	bool coalesced;
+	extent = extent_try_coalesce(tsdn, arena, r_extent_hooks, rtree_ctx,
+	    extents, extent, &coalesced);
+	extent_state_set(extent, extents_state_get(extents));
+
+	if (!coalesced) {
+		return true;
+	}
+	extents_insert_locked(tsdn, extents, extent, true);
+	return false;
+}
+
 extent_t *
-extents_evict(tsdn_t *tsdn, extents_t *extents, size_t npages_min) {
+extents_evict(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
+    extents_t *extents, size_t npages_min) {
+	rtree_ctx_t rtree_ctx_fallback;
+	rtree_ctx_t *rtree_ctx = tsdn_rtree_ctx(tsdn, &rtree_ctx_fallback);
+
 	malloc_mutex_lock(tsdn, &extents->mtx);
 
-	/* Get the LRU extent, if any. */
-	extent_t *extent = extent_list_first(&extents->lru);
-	if (extent == NULL) {
-		goto label_return;
-	}
-	/* Check the eviction limit. */
-	size_t npages = extent_size_get(extent) >> LG_PAGE;
-	if (atomic_read_zu(&extents->npages) - npages < npages_min) {
-		extent = NULL;
-		goto label_return;
+	/*
+	 * Get the LRU coalesced extent, if any.  If coalescing was delayed,
+	 * the loop will iterate until the LRU extent is fully coalesced.
+	 */
+	extent_t *extent;
+	while (true) {
+		/* Get the LRU extent, if any. */
+		extent = extent_list_first(&extents->lru);
+		if (extent == NULL) {
+			goto label_return;
+		}
+		/* Check the eviction limit. */
+		size_t npages = extent_size_get(extent) >> LG_PAGE;
+		if (atomic_read_zu(&extents->npages) - npages < npages_min) {
+			extent = NULL;
+			goto label_return;
+		}
+		extents_remove_locked(tsdn, extents, extent, false);
+		if (!extents->delay_coalesce) {
+			break;
+		}
+		/* Try to coalesce. */
+		if (extent_try_delayed_coalesce(tsdn, arena, r_extent_hooks,
+		    rtree_ctx, extents, extent)) {
+			break;
+		}
+		/*
+		 * The LRU extent was just coalesced and the result placed in
+		 * the LRU at its neighbor's position.  Start over.
+		 */
 	}
-	extents_remove_locked(tsdn, extents, extent);
 
 	/*
 	 * Either mark the extent active or deregister it to protect against
@@ -320,29 +369,29 @@ extents_postfork_child(tsdn_t *tsdn, extents_t *extents) {
 
 static void
 extent_deactivate_locked(tsdn_t *tsdn, arena_t *arena, extents_t *extents,
-    extent_t *extent) {
+    extent_t *extent, bool preserve_lru) {
 	assert(extent_arena_get(extent) == arena);
 	assert(extent_state_get(extent) == extent_state_active);
 
 	extent_state_set(extent, extents_state_get(extents));
-	extents_insert_locked(tsdn, extents, extent);
+	extents_insert_locked(tsdn, extents, extent, preserve_lru);
 }
 
 static void
 extent_deactivate(tsdn_t *tsdn, arena_t *arena, extents_t *extents,
-    extent_t *extent) {
+    extent_t *extent, bool preserve_lru) {
 	malloc_mutex_lock(tsdn, &extents->mtx);
-	extent_deactivate_locked(tsdn, arena, extents, extent);
+	extent_deactivate_locked(tsdn, arena, extents, extent, preserve_lru);
 	malloc_mutex_unlock(tsdn, &extents->mtx);
 }
 
 static void
 extent_activate_locked(tsdn_t *tsdn, arena_t *arena, extents_t *extents,
-    extent_t *extent) {
+    extent_t *extent, bool preserve_lru) {
 	assert(extent_arena_get(extent) == arena);
 	assert(extent_state_get(extent) == extents_state_get(extents));
 
-	extents_remove_locked(tsdn, extents, extent);
+	extents_remove_locked(tsdn, extents, extent, preserve_lru);
 	extent_state_set(extent, extent_state_active);
 }
 
@@ -581,7 +630,7 @@ extent_recycle_extract(tsdn_t *tsdn, arena_t *arena,
 		return NULL;
 	}
 
-	extent_activate_locked(tsdn, arena, extents, extent);
+	extent_activate_locked(tsdn, arena, extents, extent, false);
 	if (!locked) {
 		malloc_mutex_unlock(tsdn, &extents->mtx);
 	}
@@ -620,7 +669,7 @@ extent_recycle_split(tsdn_t *tsdn, arena_t *arena,
 			    lead);
 			return NULL;
 		}
-		extent_deactivate(tsdn, arena, extents, lead);
+		extent_deactivate(tsdn, arena, extents, lead, false);
 	}
 
 	/* Split the trail. */
@@ -633,7 +682,7 @@ extent_recycle_split(tsdn_t *tsdn, arena_t *arena,
 			    extent);
 			return NULL;
 		}
-		extent_deactivate(tsdn, arena, extents, trail);
+		extent_deactivate(tsdn, arena, extents, trail, false);
 	} else if (leadsize == 0) {
 		/*
 		 * Splitting causes usize to be set as a side effect, but no
@@ -1030,7 +1079,16 @@ extent_coalesce(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
     extents_t *extents, extent_t *inner, extent_t *outer, bool forward) {
 	assert(extent_can_coalesce(arena, extents, inner, outer));
 
-	extent_activate_locked(tsdn, arena, extents, outer);
+	if (forward && extents->delay_coalesce) {
+		/*
+		 * The extent that remains after coalescing must occupy the
+		 * outer extent's position in the LRU.  For forward coalescing,
+		 * swap the inner extent into the LRU.
+		 */
+		extent_list_replace(&extents->lru, outer, inner);
+	}
+	extent_activate_locked(tsdn, arena, extents, outer,
+	    extents->delay_coalesce);
 
 	malloc_mutex_unlock(tsdn, &extents->mtx);
 	bool err = extent_merge_wrapper(tsdn, arena, r_extent_hooks,
@@ -1038,7 +1096,11 @@ extent_coalesce(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
 	malloc_mutex_lock(tsdn, &extents->mtx);
 
 	if (err) {
-		extent_deactivate_locked(tsdn, arena, extents, outer);
+		if (forward && extents->delay_coalesce) {
+			extent_list_replace(&extents->lru, inner, outer);
+		}
+		extent_deactivate_locked(tsdn, arena, extents, outer,
+		    extents->delay_coalesce);
 	}
 
 	return err;
@@ -1047,14 +1109,14 @@ extent_coalesce(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
 static extent_t *
 extent_try_coalesce(tsdn_t *tsdn, arena_t *arena,
     extent_hooks_t **r_extent_hooks, rtree_ctx_t *rtree_ctx, extents_t *extents,
-    extent_t *extent) {
+    extent_t *extent, bool *coalesced) {
 	/*
 	 * Continue attempting to coalesce until failure, to protect against
 	 * races with other threads that are thwarted by this one.
 	 */
-	bool coalesced;
+	bool again;
 	do {
-		coalesced = false;
+		again = false;
 
 		/* Try to coalesce forward. */
 		rtree_elm_t *next_elm = rtree_elm_acquire(tsdn, &extents_rtree,
@@ -1073,7 +1135,12 @@ extent_try_coalesce(tsdn_t *tsdn, arena_t *arena,
 			rtree_elm_release(tsdn, &extents_rtree, next_elm);
 			if (can_coalesce && !extent_coalesce(tsdn, arena,
 			    r_extent_hooks, extents, extent, next, true)) {
-				coalesced = true;
+				if (extents->delay_coalesce) {
+					/* Do minimal coalescing. */
+					*coalesced = true;
+					return extent;
+				}
+				again = true;
 			}
 		}
 
@@ -1090,11 +1157,19 @@ extent_try_coalesce(tsdn_t *tsdn, arena_t *arena,
 			if (can_coalesce && !extent_coalesce(tsdn, arena,
 			    r_extent_hooks, extents, extent, prev, false)) {
 				extent = prev;
-				coalesced = true;
+				if (extents->delay_coalesce) {
+					/* Do minimal coalescing. */
+					*coalesced = true;
+					return extent;
+				}
+				again = true;
 			}
 		}
-	} while (coalesced);
+	} while (again);
 
+	if (extents->delay_coalesce) {
+		*coalesced = false;
+	}
 	return extent;
 }
 
@@ -1118,12 +1193,12 @@ extent_record(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
 
 	assert(extent_lookup(tsdn, extent_base_get(extent), true) == extent);
 
-	if (extents->try_coalesce) {
+	if (!extents->delay_coalesce) {
 		extent = extent_try_coalesce(tsdn, arena, r_extent_hooks,
-		    rtree_ctx, extents, extent);
+		    rtree_ctx, extents, extent, NULL);
 	}
 
-	extent_deactivate_locked(tsdn, arena, extents, extent);
+	extent_deactivate_locked(tsdn, arena, extents, extent, false);
 
 	malloc_mutex_unlock(tsdn, &extents->mtx);
 }