From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754892AbaIKOdW (ORCPT ); Thu, 11 Sep 2014 10:33:22 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:51330 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752376AbaIKOdV (ORCPT ); Thu, 11 Sep 2014 10:33:21 -0400 From: "Rafael J. Wysocki" To: Michal Hocko Cc: Tejun Heo , Cong Wang , LKML , David Rientjes , Andrew Morton Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen Date: Thu, 11 Sep 2014 16:52:50 +0200 Message-ID: <23520581.7q253rZGaa@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.16.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <20140911142822.GL22042@dhcp22.suse.cz> References: <1409869842-10807-1-git-send-email-xiyou.wangcong@gmail.com> <1973496.9q6IzlQu6V@vostro.rjw.lan> <20140911142822.GL22042@dhcp22.suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday, September 11, 2014 04:28:22 PM Michal Hocko wrote: > On Thu 11-09-14 16:32:50, Rafael J. Wysocki wrote: > > On Thursday, September 11, 2014 04:10:51 PM Michal Hocko wrote: > > > On Thu 11-09-14 16:26:56, Rafael J. Wysocki wrote: > > > > On Thursday, September 11, 2014 04:04:48 PM Michal Hocko wrote: > > > > > On Thu 11-09-14 16:17:56, Rafael J. Wysocki wrote: > > > > > [...] > > > > > > And I'm still wondering if the OOM killer may be made avoid killing frozen > > > > > > tasks. > > > > > > > > > > This is really tricky. OOM killer aims at the biggest memory hog. We > > > > > shouldn't ignore it just because it hides into the fridge... So even > > > > > if we "fix" oom killer to ignore frozen tasks (which is inherently > > > > > racy btw.) then we have a potential problem of freezer abuse (e.g. in > > > > > container environments). So I strongly believe that the OOM killer has > > > > > to be able to kill a frozen tasks. > > > > > > > > OK > > > > > > > > Is the OOM killer the only place where TIF_MEMDIE is set? > > > > > > Yes. To be precise, lowmemorykiller (staging android thingy), global OOM > > > killer and memcg OOM killer. Any other users would be an abuse. > > > > OK > > > > So can we ensure that those things don't trigger during system suspend (or > > equivalent) and then simply use the TIF_MEMDIE check in __refrigerator()? > > That would require that no memory allocation triggers OOM killer during > suspend. I don't think this will work out. OOM killer is the last resort > action. We cannot simply give access to memory reserves just because the > current context is in the middle of suspend. But we can fail the allocation, can't we? > What is the worst thing that might happen when a task is killed in the > middle of suspend? I thought that suspend would fail after several > attempts to suspend all existing tasks. The problem is what to do when we need to kill a frozen task. In that case we need to thaw it and then it will die eventually. Unfortunately, it generally can do something undesirable before dying. That may be accessing a suspended device, for example. Rafael