diff -r 9259fdc3570c memory/jemalloc/jemalloc.c
--- a/memory/jemalloc/jemalloc.c	Wed Jan 27 16:20:05 2010 -0800
+++ b/memory/jemalloc/jemalloc.c	Wed Jan 27 23:03:56 2010 -0600
@@ -373,7 +373,7 @@
 static const bool __isthreaded = true;
 #endif
 
-#if defined(MOZ_MEMORY_SOLARIS) && defined(MAP_ALIGN) && !defined(JEMALLOC_NEVER_USES_MAP_ALIGN)
+#if defined(MOZ_MEMORY_SOLARIS) || defined(MOZ_MEMORY_LINUX) || defined(MOZ_MEMORY_BSD)
 #define JEMALLOC_USES_MAP_ALIGN	 /* Required on Solaris 10. Might improve performance elsewhere. */
 #endif
 
@@ -2178,20 +2178,31 @@
 	 * We don't use MAP_FIXED here, because it can cause the *replacement*
 	 * of existing mappings, and we only want to create new mappings.
 	 */
-#ifdef MALLOC_PAGEFILE
-	if (pfd != -1) {
-		ret = mmap((void *)alignment, size, PROT_READ | PROT_WRITE, MAP_PRIVATE |
-		    MAP_NOSYNC | MAP_ALIGN, pfd, 0);
-	} else
-#endif
-	       {
-		ret = mmap((void *)alignment, size, PROT_READ | PROT_WRITE, MAP_PRIVATE |
-		    MAP_NOSYNC | MAP_ALIGN | MAP_ANON, -1, 0);
-	}
+	ret = mmap(NULL, size + alignment, PROT_READ | PROT_WRITE, MAP_PRIVATE |
+		    MAP_NOSYNC| MAP_ANON, -1, 0);
 	assert(ret != NULL);
 
 	if (ret == MAP_FAILED)
 		ret = NULL;
+	else {
+		uintptr_t aligned_ret;
+		size_t extra_size;
+
+		aligned_ret = (uintptr_t)ret + alignment - 1;
+		aligned_ret &= ~(alignment - 1);
+		extra_size = aligned_ret - (uintptr_t)ret;
+		munmap(ret, extra_size);
+		munmap(ret + extra_size + size, alignment - extra_size);
+		ret = (void *)aligned_ret;
+#ifdef MALLOC_PAGEFILE
+		if (pfd != -1) {
+			ret = mmap(ret, size, PROT_READ | PROT_WRITE, MAP_PRIVATE |
+			    MAP_NOSYNC | MAP_FIXED, pfd, 0);
+		}
+		if (ret == MAP_FAILED)
+			ret = NULL;
+#endif
+	}
 	return (ret);
 }
 #endif