From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751887AbcBFIiD (ORCPT ); Sat, 6 Feb 2016 03:38:03 -0500 Received: from mail-wm0-f67.google.com ([74.125.82.67]:36199 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751769AbcBFIiA (ORCPT ); Sat, 6 Feb 2016 03:38:00 -0500 Date: Sat, 6 Feb 2016 09:37:58 +0100 From: Michal Hocko To: Tetsuo Handa Cc: akpm@linux-foundation.org, rientjes@google.com, mgorman@suse.de, oleg@redhat.com, torvalds@linux-foundation.org, hughd@google.com, andrea@kernel.org, riel@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 5/5] mm, oom_reaper: implement OOM victims queuing Message-ID: <20160206083757.GB25220@dhcp22.suse.cz> References: <1454505240-23446-1-git-send-email-mhocko@kernel.org> <1454505240-23446-6-git-send-email-mhocko@kernel.org> <201602041949.BIG30715.QVFLFOOOHMtSFJ@I-love.SAKURA.ne.jp> <20160204145357.GE14425@dhcp22.suse.cz> <201602061454.GDG43774.LSHtOOMFOFVJQF@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201602061454.GDG43774.LSHtOOMFOFVJQF@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 06-02-16 14:54:24, Tetsuo Handa wrote: > Michal Hocko wrote: > > > But if we consider non system-wide OOM events, it is not very unlikely to hit > > > this race. This queue is useful for situations where memcg1 and memcg2 hit > > > memcg OOM at the same time and victim1 in memcg1 cannot terminate immediately. > > > > This can happen of course but the likelihood is _much_ smaller without > > the global OOM because the memcg OOM killer is invoked from a lockless > > context so the oom context cannot block the victim to proceed. > > Suppose mem_cgroup_out_of_memory() is called from a lockless context via > mem_cgroup_oom_synchronize() called from pagefault_out_of_memory(), that > "lockless" is talking about only current thread, doesn't it? Yes and you need the OOM context to sit on the same lock as the victim to form a deadlock. So while the victim might be blocked somewhere it is much less likely it would be deadlocked. > Since oom_kill_process() sets TIF_MEMDIE on first mm!=NULL thread of a > victim process, it is possible that non-first mm!=NULL thread triggers > pagefault_out_of_memory() and first mm!=NULL thread gets TIF_MEMDIE, > isn't it? I got lost here completely. Maybe it is your usage of thread terminology again. > Then, where is the guarantee that victim1 (first mm!=NULL thread in memcg1 > which got TIF_MEMDIE) is not waiting at down_read(&victim2->mm->mmap_sem) > when victim2 (first mm!=NULL thread in memcg2 which got TIF_MEMDIE) is > waiting at down_write(&victim2->mm->mmap_sem) All threads/processes sharing the same mm are in fact in the same memory cgroup. That is the reason we have owner in the task_struct > or both victim1 and victim2 > are waiting on a lock somewhere in memory reclaim path (e.g. > mutex_lock(&inode->i_mutex))? Such waiting has to make a forward progress at some point in time because the lock itself cannot be deadlocked by the memcg OOM context. -- Michal Hocko SUSE Labs