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Sat, 14 Nov 2026 15:02:22 -0800 (PST) Received: from [172.18.0.3] ([216.139.163.93]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1b505b5bf76sm15078205c88.10.2026.11.14.15.02.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Nov 2026 15:02:20 -0800 (PST) Date: Sat, 14 Nov 2026 15:02:01 -0800 From: Chris Down To: Marco Elver Cc: Alexander Potapenko , Dmitry Vyukov , Andrew Morton , Jonathan Corbet , Shuah Khan , Randy Dunlap , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH] kfence: Allow selecting static keys mode at boot In-Reply-To: References: X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Message-ID: <20261114150201.d428c3847d573be1@chrisdown.name> User-Agent: Mutt/2.4.3 (cc9e3943) (2026-10-09) Hi Marco, Marco Elver writes: >On which systems have you found static keys to provide a significant >improvement? Can you share benchmarks? I don't have numbers that show a significant improvement. To be clear, the hosts that use static keys have had it set that way since long before I started looking at this, so it may well just be cargo culted by now :-) Given that, I had a go at measuring the saving on its own. It's there, but it's small. From a quick check I did in an 8 CPU x86 VM, a kmem_cache_alloc()/kmem_cache_free() pair takes 8.0ns in static keys mode, which is the same as with KFENCE off. With the dynamic branch it takes 8.4ns. A kmalloc()/kfree() pair takes 13.3ns in all three. Both are the same with either branch layout. So static keys saves about half a nanosecond per allocation at best, in a loop that does nothing else. At a million allocations a second on a CPU, that accounts for 0.05% of it. >IMHO, I was thinking of deleting the CONFIG_KFENCE_STATIC_KEYS mode, >because on most systems, it's not worth the complexity for the small >(if any) performance improvement anymore. I agree, and I think the numbers above are enough evidence for that. Deleting it is better than this patch, because all we want is one kernel across the fleet, and that gets us there with less code. I'm happy to send the removal, if you'd like. Thanks! Chris