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Wed, 8 Aug 2018 11:11:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=virtuozzo.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=SaCo9MC6lne0n8PfH0evLVK7bfF4iBw9H1R/2C/c4oE=; b=USjH6eNdnjSosgt6XSSM/Prse/yZhVkb1eGdfcoDDP8XshVlbB8vIZ3M9HkHf2U3vTirQxImlK5XQKI+wQ3eLNaPYArR0na2tbe0tDhazoAGLKWA478vxk5RC23ACqmjX4VT0eDlk2+15h/F0h1H1MHVfQ4iDcGPaG+iqKFk/o8= Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=ktkhai@virtuozzo.com; Received: from [172.16.25.169] (185.231.240.5) by DB6PR0801MB2023.eurprd08.prod.outlook.com (2603:10a6:4:76::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.1017.15; Wed, 8 Aug 2018 12:51:15 +0000 Subject: Re: [PATCH RFC 02/10] mm: Make shrink_slab() lockless To: Tetsuo Handa Cc: mhocko@suse.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, vdavydov.dev@gmail.com References: <153365347929.19074.12509495712735843805.stgit@localhost.localdomain> <153365626605.19074.16202958374930777592.stgit@localhost.localdomain> <591d2063-0511-103d-bef6-dd35f55afe32@virtuozzo.com> From: Kirill Tkhai Message-ID: <411e77ce-90a6-8af6-dd57-bd3b6804beff@virtuozzo.com> Date: Wed, 8 Aug 2018 15:51:11 +0300 User-Agent: Mozilla/5.0 (X11; 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>> >> down_write(&shrinker_rwsem); >> - /* This may call shrinker, so it must use down_read_trylock() */ >> id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL); >> if (id < 0) >> goto unlock; > > I don't know why perf reports down_read_trylock(&shrinker_rwsem). This happens in the case of many cgroups and mounts on node. This is often happen on the big machines with containers. > But above code is already bad. GFP_KERNEL allocation involves shrinkers and > the OOM killer would be invoked because shrinkers are defunctional due to > this down_write(&shrinker_rwsem). Please avoid blocking memory allocation > with shrinker_rwsem held. There was non-blocking allocation in first versions of the patchset, but it's gone away in the process of the review (CC Vladimir). There are still pages lists shrinkers in case of shrink_slab() is not available, while additional locks makes the code more difficult and not worth this difficulties. Kirill