From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 751CBC43461 for ; Tue, 8 Sep 2020 15:36:49 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E0DD823D39 for ; Tue, 8 Sep 2020 15:36:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E0DD823D39 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 594336B0003; Tue, 8 Sep 2020 11:36:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 543476B005C; Tue, 8 Sep 2020 11:36:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 432AE6B005D; Tue, 8 Sep 2020 11:36:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0064.hostedemail.com [216.40.44.64]) by kanga.kvack.org (Postfix) with ESMTP id 29E5C6B0003 for ; Tue, 8 Sep 2020 11:36:48 -0400 (EDT) Received: from smtpin10.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id E6D45181AEF07 for ; Tue, 8 Sep 2020 15:36:47 +0000 (UTC) X-FDA: 77240296854.10.limit80_15126db270d5 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin10.hostedemail.com (Postfix) with ESMTP id B265C16A047 for ; Tue, 8 Sep 2020 15:36:47 +0000 (UTC) X-HE-Tag: limit80_15126db270d5 X-Filterd-Recvd-Size: 2947 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Tue, 8 Sep 2020 15:36:47 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id A93B9AC26; Tue, 8 Sep 2020 15:36:46 +0000 (UTC) Subject: Re: [PATCH RFC 00/10] KFENCE: A low-overhead sampling-based memory safety error detector To: Marco Elver , Dave Hansen Cc: 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, 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> <20200908153102.GB61807@elver.google.com> From: Vlastimil Babka Message-ID: Date: Tue, 8 Sep 2020 17:36:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200908153102.GB61807@elver.google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: B265C16A047 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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 9/8/20 5:31 PM, Marco Elver wrote: >> >> How much memory overhead does this end up having? I know it depends on >> the object size and so forth. But, could you give some real-world >> examples of memory consumption? Also, what's the worst case? Say I >> have a ton of worst-case-sized (32b) slab objects. Will I notice? > > KFENCE objects are limited (default 255). If we exhaust KFENCE's memory > pool, no more KFENCE allocations will occur. > Documentation/dev-tools/kfence.rst gives a formula to calculate the > KFENCE pool size: > > The total memory dedicated to the KFENCE memory pool can be computed as:: > > ( #objects + 1 ) * 2 * PAGE_SIZE > > Using the default config, and assuming a page size of 4 KiB, results in > dedicating 2 MiB to the KFENCE memory pool. > > Does that clarify this point? Or anything else that could help clarify > this? Hmm did you observe that with this limit, a long-running system would eventually converge to KFENCE memory pool being filled with long-aged objects, so there would be no space to sample new ones? > Thanks, > -- Marco >