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.

include/jemalloc/internal/extent_externs.h

@@ -18,10 +18,11 @@ size_t	extent_size_quantize_ceil(size_t size);
 ph_proto(, extent_heap_, extent_heap_t, extent_t)
 
 bool extents_init(tsdn_t *tsdn, extents_t *extents, extent_state_t state,
-    bool try_coalesce);
+    bool delay_coalesce);
 extent_state_t extents_state_get(const extents_t *extents);
 size_t extents_npages_get(extents_t *extents);
-extent_t *extents_evict(tsdn_t *tsdn, extents_t *extents, size_t npages_min);
+extent_t *extents_evict(tsdn_t *tsdn, arena_t *arena,
+    extent_hooks_t **r_extent_hooks, extents_t *extents, size_t npages_min);
 void extents_prefork(tsdn_t *tsdn, extents_t *extents);
 void extents_postfork_parent(tsdn_t *tsdn, extents_t *extents);
 void extents_postfork_child(tsdn_t *tsdn, extents_t *extents);

include/jemalloc/internal/extent_inlines.h

@@ -37,6 +37,8 @@ void extent_list_init(extent_list_t *list);
 extent_t *extent_list_first(const extent_list_t *list);
 extent_t *extent_list_last(const extent_list_t *list);
 void extent_list_append(extent_list_t *list, extent_t *extent);
+void extent_list_replace(extent_list_t *list, extent_t *to_remove,
+    extent_t *to_insert);
 void extent_list_remove(extent_list_t *list, extent_t *extent);
 int	extent_sn_comp(const extent_t *a, const extent_t *b);
 int	extent_ad_comp(const extent_t *a, const extent_t *b);
@@ -253,6 +255,13 @@ extent_list_append(extent_list_t *list, extent_t *extent) {
 	ql_tail_insert(list, extent, ql_link);
 }
 
+JEMALLOC_INLINE void
+extent_list_replace(extent_list_t *list, extent_t *to_remove,
+    extent_t *to_insert) {
+	ql_after_insert(to_remove, to_insert, ql_link);
+	ql_remove(list, to_remove, ql_link);
+}
+
 JEMALLOC_INLINE void
 extent_list_remove(extent_list_t *list, extent_t *extent) {
 	ql_remove(list, extent, ql_link);

include/jemalloc/internal/extent_structs.h

@@ -116,8 +116,11 @@ struct extents_s {
 	/* All stored extents must be in the same state. */
 	extent_state_t		state;
 
-	/* If true, try to coalesce during extent deallocation. */
-	bool			try_coalesce;
+	/*
+	 * If true, delay coalescing until eviction; otherwise coalesce during
+	 * deallocation.
+	 */
+	bool			delay_coalesce;
 };
 
 #endif /* JEMALLOC_INTERNAL_EXTENT_STRUCTS_H */

include/jemalloc/internal/private_symbols.txt

@@ -159,8 +159,10 @@ extent_init
 extent_last_get
 extent_list_append
 extent_list_first
+extent_list_init
 extent_list_last
 extent_list_remove
+extent_list_replace
 extent_lookup
 extent_merge_wrapper
 extent_past_get