From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751265AbdFUNSz (ORCPT ); Wed, 21 Jun 2017 09:18:55 -0400 Received: from mx2.suse.de ([195.135.220.15]:59087 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751114AbdFUNSy (ORCPT ); Wed, 21 Jun 2017 09:18:54 -0400 Date: Wed, 21 Jun 2017 15:18:50 +0200 From: Michal Hocko To: David Rientjes Cc: Tetsuo Handa , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm,oom_kill: Close race window of needlessly selecting new victims. Message-ID: <20170621131850.GA27494@dhcp22.suse.cz> References: <20170615103909.GG1486@dhcp22.suse.cz> <20170615214133.GB20321@dhcp22.suse.cz> <201706162122.ACE95321.tOFLOOVFFHMSJQ@I-love.SAKURA.ne.jp> <20170616141255.GN30580@dhcp22.suse.cz> <201706171417.JHG48401.JOQLHMFSVOOFtF@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 20-06-17 15:12:55, David Rientjes wrote: [...] > This doesn't prevent serial oom killing for either the system oom killer > or for the memcg oom killer. > > The oom killer cannot detect tsk_is_oom_victim() if the task has either > been removed from the tasklist or has already done cgroup_exit(). For > memcg oom killings in particular, cgroup_exit() is usually called very > shortly after the oom killer has sent the SIGKILL. If the oom reaper does > not fail (for example by failing to grab mm->mmap_sem) before another > memcg charge after cgroup_exit(victim), additional processes are killed > because the iteration does not view the victim. > > This easily kills all processes attached to the memcg with no memory > freeing from any victim. It took me some time to decrypt the above but you are right. Pinning mm_users will prevent exit path to exit_mmap and that can indeed cause another premature oom killing because the task might be unhashed or removed from the memcg before the oom reaper has a chance to reap the task. Thanks for pointing this out. This means that we either have to reimplement the unhashing/cgroup_exit for oom victims or get back to allowing oom reaper to race with exit_mmap. The later sounds much more easier to me. I was offline last two days but I will revisit my original idea ASAP. -- Michal Hocko SUSE Labs