From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f170.google.com (mail-io0-f170.google.com [209.85.223.170]) by kanga.kvack.org (Postfix) with ESMTP id 97729440441 for ; Sat, 6 Feb 2016 00:54:40 -0500 (EST) Received: by mail-io0-f170.google.com with SMTP id g73so150365290ioe.3 for ; Fri, 05 Feb 2016 21:54:40 -0800 (PST) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [2001:e42:101:1:202:181:97:72]) by mx.google.com with ESMTPS id s205si9164845ios.148.2016.02.05.21.54.39 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 05 Feb 2016 21:54:39 -0800 (PST) Subject: Re: [PATCH 5/5] mm, oom_reaper: implement OOM victims queuing From: Tetsuo Handa 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> In-Reply-To: <20160204145357.GE14425@dhcp22.suse.cz> Message-Id: <201602061454.GDG43774.LSHtOOMFOFVJQF@I-love.SAKURA.ne.jp> Date: Sat, 6 Feb 2016 14:54:24 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@kernel.org 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 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? 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? 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) or both victim1 and victim2 are waiting on a lock somewhere in memory reclaim path (e.g. mutex_lock(&inode->i_mutex))? -- 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