[PATCH v2 2/6] mm/slab: Enable SLAB_FREELIST_RANDOM by default

[Chris Down <chris@chrisdown.name>]

SLAB_FREELIST_RANDOM randomises the order in which the objects in a new
slab are handed out. Like SLAB_FREELIST_HARDENED, most distros already
enable it, and its cost is only paid when a new slab is set up.

With it on, the same system level benchmarks didn't change measurably.
Allocating from new slabs does get slower, by up to about 30% per object
in a microbenchmark which does little else.

So let's enable it by default too. SHUFFLE_PAGE_ALLOCATOR defaults to
SLAB_FREELIST_RANDOM && ACPI_NUMA, so it's now built in by default on
those systems, but page shuffling itself stays off unless it's enabled
with page_alloc.shuffle.

Suggested-by: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Chris Down <chris@chrisdown.name>
---
 mm/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index 17d017e8fbef..92ff97ff24fb 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -200,6 +200,7 @@ config SLAB_MERGE_DEFAULT
 config SLAB_FREELIST_RANDOM
 	bool "Randomize slab freelist"
 	depends on !SLUB_TINY
+	default y
 	help
 	  Randomizes the freelist order used on creating new pages. This
 	  security feature reduces the predictability of the kernel slab
-- 
2.54.0