--- a/memory/jemalloc/jemalloc.c
+++ b/memory/jemalloc/jemalloc.c
@@ -169,17 +169,17 @@
    /*
     * MALLOC_PAGEFILE causes all mmap()ed memory to be backed by temporary
     * files, so that if a chunk is mapped, it is guaranteed to be swappable.
     * This avoids asynchronous OOM failures that are due to VM over-commit.
     *
     * XXX OS X over-commits, so we should probably use mmap() instead of
     * vm_allocate(), so that MALLOC_PAGEFILE works.
     */
-//#  define MALLOC_PAGEFILE
+#define MALLOC_PAGEFILE
 #endif
 
 #ifdef MALLOC_PAGEFILE
 /* Write size when initializing a page file. */
 #  define MALLOC_PAGEFILE_WRITE_SIZE 512
 #endif
 
 #ifdef MOZ_MEMORY_LINUX