Enable both sbrk(2)- and mmap(2)-based memory acquisition methods by

default.  This has the disadvantage of rendering the datasize resource
limit irrelevant, but without this change, legitimate uses of more
memory than will fit in the data segment are thwarted by default.

Fix chunk_alloc_mmap() to work correctly if initial mapping is not
chunk-aligned and mapping extension fails.

2 files changed, 20 insertions, 19 deletions

diff --git a/lib/libc/stdlib/malloc.3 b/lib/libc/stdlib/malloc.3
index 7138ead..466accc 100644
--- a/lib/libc/stdlib/malloc.3
+++ b/lib/libc/stdlib/malloc.3
@@ -32,7 +32,7 @@
 .\"     @(#)malloc.3	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd December 27, 2007
+.Dd January 3, 2008
 .Dt MALLOC 3
 .Os
 .Sh NAME
@@ -245,7 +245,7 @@ This option is not available for some configurations (non-PIC).
 Use
 .Xr mmap 2
 to acquire anonymously mapped memory.
-This option is disabled by default.
+This option is enabled by default.
 If both the
 .Dq D
 and
@@ -335,24 +335,24 @@ Traditionally, allocators have used
 to obtain memory, which is suboptimal for several reasons, including race
 conditions, increased fragmentation, and artificial limitations on maximum
 usable memory.
-This allocator uses
-.Xr sbrk 2
-by default in order to facilitate resource limits, but it can be configured at
-run time to use
+This allocator uses both
 .Xr sbrk 2
-and/or
-.Xr mmap 2 .
+and
+.Xr mmap 2
+by default, but it can be configured at run time to use only one or the other.
 If resource limits are not a primary concern, the preferred configuration is
 .Ev MALLOC_OPTIONS=dM
 or
 .Ev MALLOC_OPTIONS=DM .
 When so configured, the
 .Ar datasize
-resource limit has little practical effect for typical applications.
-The
+resource limit has little practical effect for typical applications; use
+.Ev MALLOC_OPTIONS=Dm
+if that is a concern.
+Regardless of allocator configuration, the
 .Ar vmemoryuse
-resource limit, however, can be used to bound the total virtual memory used by
-a process, as described in
+resource limit can be used to bound the total virtual memory used by a
+process, as described in
 .Xr limits 1 .
 .Pp
 This allocator uses multiple arenas in order to reduce lock contention for
diff --git a/lib/libc/stdlib/malloc.c b/lib/libc/stdlib/malloc.c
index 5c987c5..abe367a 100644
--- a/lib/libc/stdlib/malloc.c
+++ b/lib/libc/stdlib/malloc.c
@@ -1,5 +1,5 @@
 /*-
- * Copyright (C) 2006,2007 Jason Evans <jasone@FreeBSD.org>.
+ * Copyright (C) 2006-2008 Jason Evans <jasone@FreeBSD.org>.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -131,7 +131,7 @@
  * unnecessary, but we are burdened by history and the lack of resource limits
  * for anonymous mapped memory.
  */
-#define MALLOC_DSS
+#define	MALLOC_DSS
 
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
@@ -821,7 +821,7 @@ static bool	opt_junk = false;
 #endif
 #ifdef MALLOC_DSS
 static bool	opt_dss = true;
-static bool	opt_mmap = false;
+static bool	opt_mmap = true;
 #endif
 static bool	opt_hint = false;
 #ifdef MALLOC_LAZY_FREE
@@ -1646,6 +1646,7 @@ chunk_alloc_mmap(size_t size)
 				return (NULL);
 
 			/* Clean up unneeded leading/trailing space. */
+			offset = CHUNK_ADDR2OFFSET(ret);
 			if (offset != 0) {
 				/* Leading space. */
 				pages_unmap(ret, chunksize - offset);
@@ -1661,11 +1662,11 @@ chunk_alloc_mmap(size_t size)
 				pages_unmap((void *)((uintptr_t)ret + size),
 				    chunksize);
 			}
+		} else {
+			/* Clean up unneeded leading space. */
+			pages_unmap(ret, chunksize - offset);
+			ret = (void *)((uintptr_t)ret + (chunksize - offset));
 		}
-
-		/* Clean up unneeded leading space. */
-		pages_unmap(ret, chunksize - offset);
-		ret = (void *)((uintptr_t)ret + (chunksize - offset));
 	}
 
 	return (ret);