Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933275AbbLOIaZ (ORCPT ); Tue, 15 Dec 2015 03:30:25 -0500 Received: from mx2.parallels.com ([199.115.105.18]:60812 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932078AbbLOIaY (ORCPT ); Tue, 15 Dec 2015 03:30:24 -0500 Date: Tue, 15 Dec 2015 11:30:07 +0300 From: Vladimir Davydov To: Kamezawa Hiroyuki CC: Michal Hocko , Andrew Morton , Johannes Weiner , , Subject: Re: [PATCH 1/7] mm: memcontrol: charge swap to cgroup2 Message-ID: <20151215083007.GI28521@esperanza> References: <265d8fe623ed2773d69a26d302eb31e335377c77.1449742560.git.vdavydov@virtuozzo.com> <20151214153037.GB4339@dhcp22.suse.cz> <566F8528.9060205@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <566F8528.9060205@jp.fujitsu.com> X-ClientProxiedBy: US-EXCH.sw.swsoft.com (10.255.249.47) To US-EXCH.sw.swsoft.com (10.255.249.47) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2564 Lines: 52 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. Thanks, Vladimir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/