36836: zhalloc() avoids re-scanning all heaps when the last known heap with free space does not have enough space

This is the second of two performance optimizations for situations where
all heap arenas in the list are mostly full.

2 files changed, 12 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 3adb1f159..421da2f6f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,9 @@
 2015-10-11  Barton E. Schaefer  <schaefer@zsh.org>
 
-	* 36834: Src/mem.c: freeheap preserves last allocated heap
+	* 36836: Src/mem.c: zhalloc() avoids re-scanning all heaps when
+	the last known heap with free space does not have enough space
+
+	* 36834: Src/mem.c: freeheap() preserves last allocated heap
 
 2015-10-11  Frank Terbeck  <ft@bewatermyfriend.org>
 
diff --git a/Src/mem.c b/Src/mem.c
index d49f685fe..191428323 100644
--- a/Src/mem.c
+++ b/Src/mem.c
@@ -582,10 +582,14 @@ zhalloc(size_t size)
 
     /* find a heap with enough free space */
 
-    for (h = ((fheap && ARENA_SIZEOF(fheap) >= (size + fheap->used))
-	      ? fheap : heaps);
-	 h; h = h->next) {
-	hp = h;
+    /*
+     * This previously assigned:
+     *   h = ((fheap && ARENA_SIZEOF(fheap) >= (size + fheap->used))
+     *	      ? fheap : heaps);
+     * but we think that nothing upstream of fheap has more free space,
+     * so why start over at heaps just because fheap has too little?
+     */
+    for (h = (fheap ? fheap : heaps); h; h = h->next) {
 	if (ARENA_SIZEOF(h) >= (n = size + h->used)) {
 	    void *ret;