From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f171.google.com (mail-ig0-f171.google.com [209.85.213.171]) by kanga.kvack.org (Postfix) with ESMTP id 91F136B0038 for ; Tue, 15 Dec 2015 04:30:26 -0500 (EST) Received: by mail-ig0-f171.google.com with SMTP id to18so9157859igc.0 for ; Tue, 15 Dec 2015 01:30:26 -0800 (PST) Received: from mgwkm04.jp.fujitsu.com (mgwkm04.jp.fujitsu.com. [202.219.69.171]) by mx.google.com with ESMTPS id n9si29141870igv.82.2015.12.15.01.30.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 15 Dec 2015 01:30:25 -0800 (PST) Received: from m3050.s.css.fujitsu.com (msm.b.css.fujitsu.com [10.134.21.208]) by kw-mxq.gw.nic.fujitsu.com (Postfix) with ESMTP id 86635AC012F for ; Tue, 15 Dec 2015 18:30:17 +0900 (JST) Subject: Re: [PATCH 1/7] mm: memcontrol: charge swap to cgroup2 References: <265d8fe623ed2773d69a26d302eb31e335377c77.1449742560.git.vdavydov@virtuozzo.com> <20151214153037.GB4339@dhcp22.suse.cz> <566F8528.9060205@jp.fujitsu.com> <20151215083007.GI28521@esperanza> From: Kamezawa Hiroyuki Message-ID: <566FDD97.9070100@jp.fujitsu.com> Date: Tue, 15 Dec 2015 18:29:59 +0900 MIME-Version: 1.0 In-Reply-To: <20151215083007.GI28521@esperanza> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: Michal Hocko , Andrew Morton , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 2015/12/15 17:30, Vladimir Davydov wrote: > On Tue, Dec 15, 2015 at 12:12:40PM +0900, Kamezawa Hiroyuki wrote: >> On 2015/12/15 0:30, Michal Hocko wrote: >>> On Thu 10-12-15 14:39:14, Vladimir Davydov wrote: >>>> In the legacy hierarchy we charge memsw, which is dubious, because: >>>> >>>> - memsw.limit must be >= memory.limit, so it is impossible to limit >>>> swap usage less than memory usage. Taking into account the fact that >>>> the primary limiting mechanism in the unified hierarchy is >>>> memory.high while memory.limit is either left unset or set to a very >>>> large value, moving memsw.limit knob to the unified hierarchy would >>>> effectively make it impossible to limit swap usage according to the >>>> user preference. >>>> >>>> - memsw.usage != memory.usage + swap.usage, because a page occupying >>>> both swap entry and a swap cache page is charged only once to memsw >>>> counter. As a result, it is possible to effectively eat up to >>>> memory.limit of memory pages *and* memsw.limit of swap entries, which >>>> looks unexpected. >>>> >>>> That said, we should provide a different swap limiting mechanism for >>>> cgroup2. >>>> This patch adds mem_cgroup->swap counter, which charges the actual >>>> number of swap entries used by a cgroup. It is only charged in the >>>> unified hierarchy, while the legacy hierarchy memsw logic is left >>>> intact. >>> >>> I agree that the previous semantic was awkward. The problem I can see >>> with this approach is that once the swap limit is reached the anon >>> memory pressure might spill over to other and unrelated memcgs during >>> the global memory pressure. I guess this is what Kame referred to as >>> anon would become mlocked basically. This would be even more of an issue >>> with resource delegation to sub-hierarchies because nobody will prevent >>> setting the swap amount to a small value and use that as an anon memory >>> protection. >>> >>> I guess this was the reason why this approach hasn't been chosen before >> >> Yes. At that age, "never break global VM" was the policy. And "mlock" can be >> used for attacking system. > > If we are talking about "attacking system" from inside a container, > there are much easier and disruptive ways, e.g. running a fork-bomb or > creating pipes - such memory can't be reclaimed and global OOM killer > won't help. You're right. We just wanted to avoid affecting global memory reclaim by each cgroup settings. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org