Trim before commit in extent_recycle().

This avoids creating clean committed pages as a side effect of aligned
allocation.  For configurations that decommit memory, purged pages are
decommitted, and decommitted extents cannot be coalesced with committed
extents.  Unless the clean committed pages happen to be selected during
allocation, they cause unnecessary permanent extent fragmentation.

This resolves #766.

2 files changed, 9 insertions, 3 deletions

diff --git a/src/extent.c b/src/extent.c
index 6b7da3f..d08ccdb 100644
--- a/src/extent.c
+++ b/src/extent.c
@@ -829,12 +829,16 @@ extent_recycle(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
 	rtree_ctx_t rtree_ctx_fallback;
 	rtree_ctx_t *rtree_ctx = tsdn_rtree_ctx(tsdn, &rtree_ctx_fallback);
 
+	bool committed = false;
 	extent_t *extent = extent_recycle_extract(tsdn, arena, r_extent_hooks,
 	    rtree_ctx, extents, false, new_addr, size, pad, alignment, slab,
-	    zero, commit);
+	    zero, &committed);
 	if (extent == NULL) {
 		return NULL;
 	}
+	if (committed) {
+		*commit = true;
+	}
 
 	extent = extent_recycle_split(tsdn, arena, r_extent_hooks, rtree_ctx,
 	    extents, new_addr, size, pad, alignment, slab, szind, extent);
@@ -996,7 +1000,7 @@ extent_grow_retained(tsdn_t *tsdn, arena_t *arena,
 	assert(new_addr == NULL || leadsize == 0);
 	assert(alloc_size >= leadsize + esize);
 	size_t trailsize = alloc_size - leadsize - esize;
-	if (extent_zeroed_get(extent)) {
+	if (extent_zeroed_get(extent) && extent_committed_get(extent)) {
 		*zero = true;
 	}
 	if (extent_committed_get(extent)) {
diff --git a/src/extent_mmap.c b/src/extent_mmap.c
index b186275..be09937 100644
--- a/src/extent_mmap.c
+++ b/src/extent_mmap.c
@@ -15,7 +15,9 @@ extent_alloc_mmap(void *new_addr, size_t size, size_t alignment, bool *zero,
 		return NULL;
 	}
 	assert(ret != NULL);
-	*zero = true;
+	if (*commit) {
+		*zero = true;
+	}
 	return ret;
 }