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Tue, 8 Sep 2020 15:54:40 +0000 (UTC) IronPort-SDR: jsOlP98yj3d3qEvWpOxnveoEh5ixoPrWzJqgIorN00ozly3XXHA+y6Fp4WDyzZSn6u6DSxXc+P TdX4wrU7oWWw== X-IronPort-AV: E=McAfee;i="6000,8403,9738"; a="158186618" X-IronPort-AV: E=Sophos;i="5.76,406,1592895600"; d="scan'208";a="158186618" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Sep 2020 08:54:39 -0700 IronPort-SDR: T/1nXKokDV2anso0ibUdaFY4IRwHXk4XDbsdwwQVHcDxggXBHCGPbD47sN0fpoKWjY0Q8JfeEW 7rW0V0zEO1TQ== X-IronPort-AV: E=Sophos;i="5.76,406,1592895600"; d="scan'208";a="299836594" Received: from sparasa-mobl1.amr.corp.intel.com (HELO [10.251.10.231]) ([10.251.10.231]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Sep 2020 08:54:38 -0700 Subject: Re: [PATCH RFC 09/10] kfence, Documentation: add KFENCE documentation To: Marco Elver , glider@google.com, akpm@linux-foundation.org, catalin.marinas@arm.com, cl@linux.com, rientjes@google.com, iamjoonsoo.kim@lge.com, mark.rutland@arm.com, penberg@kernel.org Cc: hpa@zytor.com, paulmck@kernel.org, andreyknvl@google.com, aryabinin@virtuozzo.com, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, dvyukov@google.com, edumazet@google.com, gregkh@linuxfoundation.org, mingo@redhat.com, jannh@google.com, corbet@lwn.net, keescook@chromium.org, peterz@infradead.org, cai@lca.pw, tglx@linutronix.de, will@kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org References: <20200907134055.2878499-1-elver@google.com> <20200907134055.2878499-10-elver@google.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200907134055.2878499-10-elver@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Rspamd-Queue-Id: 6D3FD1804E3A1 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 9/7/20 6:40 AM, Marco Elver wrote: > +The most important parameter is KFENCE's sample interval, which can be= set via > +the kernel boot parameter ``kfence.sample_interval`` in milliseconds. = The > +sample interval determines the frequency with which heap allocations w= ill be > +guarded by KFENCE. The default is configurable via the Kconfig option > +``CONFIG_KFENCE_SAMPLE_INTERVAL``. Setting ``kfence.sample_interval=3D= 0`` > +disables KFENCE. > + > +With the Kconfig option ``CONFIG_KFENCE_NUM_OBJECTS`` (default 255), t= he number > +of available guarded objects can be controlled. Each object requires 2= pages, > +one for the object itself and the other one used as a guard page; obje= ct pages > +are interleaved with guard pages, and every object page is therefore s= urrounded > +by two guard pages. Is it hard to make these both tunable at runtime? It would be nice if I hit a KFENCE error on a system to bump up the number of objects and turn up the frequency of guarded objects to try to hit it again. That would be a really nice feature for development environments. It would also be nice to have a counter somewhere (/proc/vmstat?) to explicitly say how many pages are currently being used. I didn't mention it elsewhere, but this work looks really nice. It has very little impact on the core kernel and looks like a very nice tool to have in the toolbox. I don't see any major reasons we wouldn't want to merge after our typical bikeshedding. :)