improve realloc. when expanding a region, actually use the free page cache

instead of simply zapping it. this can save many syscalls in a program
that repeatedly grows and shrinks a buffer, as observed in the wild.

1 files changed, 16 insertions, 7 deletions

diff --git a/src/lib/libc/stdlib/malloc.c b/src/lib/libc/stdlib/malloc.c
index 69ae877aba..5e5dafbd17 100644
--- a/src/lib/libc/stdlib/malloc.c
+++ b/src/lib/libc/stdlib/malloc.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: malloc.c,v 1.173 2015/01/16 16:48:51 deraadt Exp $    */
+/*      $OpenBSD: malloc.c,v 1.174 2015/04/06 09:18:51 tedu Exp $       */
 /*
  * Copyright (c) 2008, 2010, 2011 Otto Moerbeek <otto@drijf.net>
  * Copyright (c) 2012 Matthew Dempsky <matthew@openbsd.org>
@@ -391,7 +391,7 @@ zapcacheregion(struct dir_info *d, void *p, size_t len)
 }
 
 static void *
-map(struct dir_info *d, size_t sz, int zero_fill)
+map(struct dir_info *d, void *hint, size_t sz, int zero_fill)
 {
         size_t psz = sz >> MALLOC_PAGESHIFT;
         struct region_info *r, *big = NULL;
@@ -405,7 +405,7 @@ map(struct dir_info *d, size_t sz, int zero_fill)
                 wrterror("map round", NULL);
                 return MAP_FAILED;
         }
-        if (psz > d->free_regions_size) {
+        if (!hint && psz > d->free_regions_size) {
                 _MALLOC_LEAVE();
                 p = MMAP(sz);
                 _MALLOC_ENTER();
@@ -418,6 +418,8 @@ map(struct dir_info *d, size_t sz, int zero_fill)
         for (i = 0; i < mopts.malloc_cache; i++) {
                 r = &d->free_regions[(i + offset) & (mopts.malloc_cache - 1)];
                 if (r->p != NULL) {
+                        if (hint && r->p != hint)
+                                continue;
                         if (r->size == psz) {
                                 p = r->p;
                                 r->p = NULL;
@@ -439,7 +441,8 @@ map(struct dir_info *d, size_t sz, int zero_fill)
         }
         if (big != NULL) {
                 r = big;
-                p = (char *)r->p + ((r->size - psz) << MALLOC_PAGESHIFT);
+                p = r->p;
+                r->p = (char *)r->p + (psz << MALLOC_PAGESHIFT);
                 if (mopts.malloc_freeunmap)
                         mprotect(p, sz, PROT_READ | PROT_WRITE);
                 if (mopts.malloc_hint)
@@ -452,6 +455,8 @@ map(struct dir_info *d, size_t sz, int zero_fill)
                         memset(p, SOME_FREEJUNK, sz);
                 return p;
         }
+        if (hint)
+                return MAP_FAILED;
         if (d->free_regions_size > mopts.malloc_cache)
                 wrterror("malloc cache", NULL);
         _MALLOC_LEAVE();
@@ -842,7 +847,7 @@ omalloc_make_chunks(struct dir_info *d, int bits, int listnum)
         int             i, k;
 
         /* Allocate a new bucket */
-        pp = map(d, MALLOC_PAGESIZE, 0);
+        pp = map(d, NULL, MALLOC_PAGESIZE, 0);
         if (pp == MAP_FAILED)
                 return NULL;
 
@@ -1071,7 +1076,7 @@ omalloc(size_t sz, int zero_fill, void *f)
                 }
                 sz += mopts.malloc_guard;
                 psz = PAGEROUND(sz);
-                p = map(pool, psz, zero_fill);
+                p = map(pool, NULL, psz, zero_fill);
                 if (p == MAP_FAILED) {
                         errno = ENOMEM;
                         return NULL;
@@ -1330,6 +1335,9 @@ orealloc(void *p, size_t newsz, void *f)
                                 size_t needed = rnewsz - roldsz;
 
                                 STATS_INC(pool->cheap_realloc_tries);
+                                q = map(pool, hint, needed, 0);
+                                if (q == hint)
+                                        goto gotit;
                                 zapcacheregion(pool, hint, needed);
                                 q = MQUERY(hint, needed);
                                 if (q == hint)
@@ -1337,6 +1345,7 @@ orealloc(void *p, size_t newsz, void *f)
                                 else
                                         q = MAP_FAILED;
                                 if (q == hint) {
+gotit:
                                         STATS_ADD(pool->malloc_used, needed);
                                         if (mopts.malloc_junk == 2)
                                                 memset(q, SOME_JUNK, needed);
@@ -1491,7 +1500,7 @@ mapalign(struct dir_info *d, size_t alignment, size_t sz, int zero_fill)
         if (alignment > SIZE_MAX - sz)
                 return MAP_FAILED;
 
-        p = map(d, sz + alignment, zero_fill);
+        p = map(d, NULL, sz + alignment, zero_fill);
         if (p == MAP_FAILED)
                 return MAP_FAILED;
         q = (char *)(((uintptr_t)p + alignment - 1) & ~(alignment - 1));