From b74d3e0c371a55cbd7aba7dc2c9f0001783aa231 Mon Sep 17 00:00:00 2001
From: Jason Evans <jasone@FreeBSD.org>
Date: Mon, 3 Nov 2008 21:17:18 +0000
Subject: [PATCH] Revert to preferring mmap(2) over sbrk(2) when mapping
 memory, due to potential extreme contention in the kernel for multi-threaded
 applications on SMP systems.

Reported by:	kris
---
 lib/libc/stdlib/malloc.3 |  2 +-
 lib/libc/stdlib/malloc.c | 29 +++++++++++++++++------------
 2 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/lib/libc/stdlib/malloc.3 b/lib/libc/stdlib/malloc.3
index 994038da0b12..a621a245b406 100644
--- a/lib/libc/stdlib/malloc.3
+++ b/lib/libc/stdlib/malloc.3
@@ -255,7 +255,7 @@ If both the
 .Dq D
 and
 .Dq M
-options are enabled, the allocator prefers the DSS over anonymous mappings,
+options are enabled, the allocator prefers anonymous mappings over the DSS,
 but allocation only fails if memory cannot be acquired via either method.
 If neither option is enabled, then the
 .Dq M
diff --git a/lib/libc/stdlib/malloc.c b/lib/libc/stdlib/malloc.c
index 00b169fa12b3..55bc4133a324 100644
--- a/lib/libc/stdlib/malloc.c
+++ b/lib/libc/stdlib/malloc.c
@@ -1536,11 +1536,6 @@ base_pages_alloc(size_t minsize)
 {
 
 #ifdef MALLOC_DSS
-	if (opt_dss) {
-		if (base_pages_alloc_dss(minsize) == false)
-			return (false);
-	}
-
 	if (opt_mmap && minsize != 0)
 #endif
 	{
@@ -1548,6 +1543,14 @@ base_pages_alloc(size_t minsize)
 			return (false);
 	}
 
+#ifdef MALLOC_DSS
+	if (opt_dss) {
+		if (base_pages_alloc_dss(minsize) == false)
+			return (false);
+	}
+
+#endif
+
 	return (true);
 }
 
@@ -1983,6 +1986,15 @@ chunk_alloc(size_t size, bool zero)
 	assert(size != 0);
 	assert((size & chunksize_mask) == 0);
 
+#ifdef MALLOC_DSS
+	if (opt_mmap)
+#endif
+	{
+		ret = chunk_alloc_mmap(size);
+		if (ret != NULL)
+			goto RETURN;
+	}
+
 #ifdef MALLOC_DSS
 	if (opt_dss) {
 		ret = chunk_recycle_dss(size, zero);
@@ -1994,14 +2006,7 @@ chunk_alloc(size_t size, bool zero)
 		if (ret != NULL)
 			goto RETURN;
 	}
-
-	if (opt_mmap)
 #endif
-	{
-		ret = chunk_alloc_mmap(size);
-		if (ret != NULL)
-			goto RETURN;
-	}
 
 	/* All strategies for allocation failed. */
 	ret = NULL;