From: Kees Cook <kees@kernel.org>
To: Chris Down <chris@chrisdown.name>
Cc: Vlastimil Babka <vbabka@kernel.org>, Harry Yoo <harry@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Hao Li <hao.li@linux.dev>, Christoph Lameter <cl@gentwo.org>,
David Rientjes <rientjes@google.com>,
Roman Gushchin <roman.gushchin@linux.dev>,
Marco Elver <elver@google.com>,
GONG Ruiqi <gongruiqi@huaweicloud.com>,
Jonathan Corbet <corbet@lwn.net>,
linux-mm@kvack.org, linux-hardening@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@meta.com
Subject: Re: [PATCH v2 2/6] mm/slab: Enable SLAB_FREELIST_RANDOM by default
Date: Fri, 30 Oct 2026 21:15:05 -0700 [thread overview]
Message-ID: <202610302113.FB347BE5@keescook> (raw)
In-Reply-To: <6bdc161bd869ead04b3b9a651ef6a83882ecbea3.1793253633.git.chris@chrisdown.name>
On Thu, Oct 29, 2026 at 02:07:55PM +0800, Chris Down wrote:
> 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>
Again, just like it should be. I wonder, though, don't these 2 changes
undercut the goal of making these boot-time selectable?
Reviewed-by: Kees Cook <kees@kernel.org>
--
Kees Cook
next prev parent reply other threads:[~2026-10-31 4:15 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-29 6:07 [PATCH v2 0/6] mm/slab: Support selecting slab hardening features at boot Chris Down
2026-10-29 6:07 ` [PATCH v2 1/6] mm/slab: Enable SLAB_FREELIST_HARDENED by default Chris Down
2026-10-31 4:13 ` Kees Cook
2026-10-29 6:07 ` [PATCH v2 2/6] mm/slab: Enable SLAB_FREELIST_RANDOM " Chris Down
2026-10-31 4:15 ` Kees Cook [this message]
2026-10-29 6:08 ` [PATCH v2 3/6] mm/slab: Support disabling SLAB_BUCKETS at boot Chris Down
2026-10-31 4:17 ` Kees Cook
2026-10-29 6:08 ` [PATCH v2 4/6] slub_kunit: Add a test for the slab_buckets boot parameter Chris Down
2026-10-31 4:22 ` Kees Cook
2026-10-29 6:09 ` [PATCH v2 5/6] mm/slab: Support disabling KMALLOC_PARTITION_CACHES at boot Chris Down
2026-10-31 4:28 ` Kees Cook
2026-10-29 6:09 ` [PATCH v2 6/6] slub_kunit: Add a test for the kmalloc_partition boot parameter Chris Down
2026-10-31 4:29 ` Kees Cook
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