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Wed, 5 May 2021 18:18:52 +0000 Date: Wed, 5 May 2021 11:18:47 -0700 From: Roman Gushchin To: Vlastimil Babka CC: Waiman Long , Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Shakeel Butt , , , Subject: Re: [PATCH v3 2/2] mm: memcg/slab: Create a new set of kmalloc-cg- caches Message-ID: References: <20210505154613.17214-1-longman@redhat.com> <20210505154613.17214-3-longman@redhat.com> <235f45b4-2d99-f32d-ac2b-18b59fea5a25@suse.cz> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <235f45b4-2d99-f32d-ac2b-18b59fea5a25@suse.cz> X-Originating-IP: [2620:10d:c090:400::5:eb2d] X-ClientProxiedBy: MWHPR01CA0048.prod.exchangelabs.com (2603:10b6:300:101::34) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.dhcp.thefacebook.com (2620:10d:c090:400::5:eb2d) by MWHPR01CA0048.prod.exchangelabs.com (2603:10b6:300:101::34) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4108.24 via Frontend Transport; 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dkim=pass header.d=fb.com header.s=facebook header.b="NyNuc/JO"; dmarc=pass (policy=reject) header.from=fb.com; spf=pass (imf02.hostedemail.com: domain of "prvs=4759a4908b=guro@fb.com" designates 67.231.153.30 as permitted sender) smtp.mailfrom="prvs=4759a4908b=guro@fb.com" X-Rspamd-Server: rspam04 X-Stat-Signature: qdu9stekqiswemdykr31u3akamjirug7 Received-SPF: none (fb.com>: No applicable sender policy available) receiver=imf02; identity=mailfrom; envelope-from=""; helo=mx0a-00082601.pphosted.com; client-ip=67.231.153.30 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620238706-277408 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 Wed, May 05, 2021 at 08:02:06PM +0200, Vlastimil Babka wrote: > On 5/5/21 7:30 PM, Roman Gushchin wrote: > > On Wed, May 05, 2021 at 11:46:13AM -0400, Waiman Long wrote: > >> > >> With this change, all the objcg pointer array objects will come from > >> KMALLOC_NORMAL caches which won't have their objcg pointer arrays. So > >> both the recursive kfree() problem and non-freeable slab problem are > >> gone. Since both the KMALLOC_NORMAL and KMALLOC_CGROUP caches no longer > >> have mixed accounted and unaccounted objects, this will slightly reduce > >> the number of objcg pointer arrays that need to be allocated and save > >> a bit of memory. > > > > Unfortunately the positive effect of this change will be likely > > reversed by a lower utilization due to a larger number of caches. > > > > Btw, I wonder if we also need a change in the slab caches merging procedure? > > KMALLOC_NORMAL caches should not be merged with caches which can potentially > > include accounted objects. > > Good point. But looks like kmalloc* caches are extempt from all merging in > create_boot_cache() via > > s->refcount = -1; /* Exempt from merging for now */ Oh, interesting... I wonder if there is (still) a good reason for that? Maybe we can remove this limitation and save some memory? > > It wouldn't hurt though to create the kmalloc-cg-* caches with SLAB_ACCOUNT flag > to prevent accidental merging in case the above is ever removed. It would also > better reflect reality, and ensure that the array is allocated immediately with > the page, AFAICS. That wouldn't be enough, because a !SLAB_ACCOUNT cache can still have accounted allocations and be merged with kmalloc-* cache. What we might wanna do is to keep the no-merging rule for kmalloc-*, but relax it for kmalloc-cg-* caches. But we can do it later, as a separate change. Thanks!