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b=RaOzfFfLGzssuh+JjOKHBZYCqFiRxq3QTgt44gt8UZ1liV6gQAY4MQTHAUCDxfOuT w6qmiQALxjw7NlwWzhRXKRELShPBy7H4rwzwz8UyGf9oG7WVa3uadE1C0BN724JkzK DZ+vJeVC/nNjYaPcC1iIVOYsfuyUj1344RQ8diH0NBhLVcRZKjDCjKHdASpQdly8bA SJXMUTzUMaY7P47tf6W/NtJCOA1nXQrUu2/Bbu4rMDoyUNzo3ewESByCgCsfk1nwrV WdwQSrSSOLn4hCph4pf9WP6uDyBMZ/AIPu5OHDZ1O+FhlsGGwircODTeQ0UblVTBwp jl4BXVE4yxqVw== Date: Fri, 30 Oct 2026 21:15:05 -0700 From: Kees Cook To: Chris Down Cc: Vlastimil Babka , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Marco Elver , GONG Ruiqi , Jonathan Corbet , 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 Message-ID: <202610302113.FB347BE5@keescook> References: <6bdc161bd869ead04b3b9a651ef6a83882ecbea3.1793253633.git.chris@chrisdown.name> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6bdc161bd869ead04b3b9a651ef6a83882ecbea3.1793253633.git.chris@chrisdown.name> X-Rspamd-Queue-Id: 1D87440002 X-Stat-Signature: 8zi4prxcpddhid5xms3qqcfc9sg349hm X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793420105-117228 X-HE-Meta: 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 VNGgMJNb EgvD6z9ncIStgygGB32XkC6ss18vMdYmX6nG3G+LoJIFR5AoQyiQBFOzgsrO4EFFkf4r9gT1PsDSfLLgRNScCuaVMePPxnl8bAnSX+GKWHVppsDkmmbm1oNZNMfYht+970m6ID10s09+OzGMSQy+dCeGWe8gvoNEAPN5Ep+X9ojL3JqyEp6pDsaqY0plPU6d4ANhsNYOTQ319N1iqBeLscBPx22sRQRTXeaOuFCMqgc/cJuLwE/Uh9caUhIYNkf4u5dEViUFFblvwHoMB5pJSxpUhpAIwi9+KVB3h3eUr9Ri8EqhysOz1Z9MO4oKo8VIcclKR Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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 > Signed-off-by: Chris Down 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 Cook