From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 20A786B0292 for ; Thu, 29 Jun 2017 14:48:07 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id z5so3611281wmz.4 for ; Thu, 29 Jun 2017 11:48:07 -0700 (PDT) Received: from mx0a-00082601.pphosted.com (mx0b-00082601.pphosted.com. [67.231.153.30]) by mx.google.com with ESMTPS id k186si9120555wmg.36.2017.06.29.11.48.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Jun 2017 11:48:05 -0700 (PDT) Date: Thu, 29 Jun 2017 14:47:48 -0400 From: Roman Gushchin Subject: Re: [v3 1/6] mm, oom: use oom_victims counter to synchronize oom victim selection Message-ID: <20170629184748.GB27714@castle> References: <1498079956-24467-1-git-send-email-guro@fb.com> <1498079956-24467-2-git-send-email-guro@fb.com> <201706220040.v5M0eSnK074332@www262.sakura.ne.jp> <20170622165858.GA30035@castle> <201706230537.IDB21366.SQHJVFOOFOMFLt@I-love.SAKURA.ne.jp> <201706230652.FDH69263.OtOLFSFMHFOQJV@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <201706230652.FDH69263.OtOLFSFMHFOQJV@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: linux-mm@kvack.org, mhocko@kernel.org, vdavydov.dev@gmail.com, hannes@cmpxchg.org, tj@kernel.org, kernel-team@fb.com, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org On Fri, Jun 23, 2017 at 06:52:20AM +0900, Tetsuo Handa wrote: > Tetsuo Handa wrote: > > Roman Gushchin wrote: > > > On Thu, Jun 22, 2017 at 09:40:28AM +0900, Tetsuo Handa wrote: > > > > Roman Gushchin wrote: > > > > > --- a/mm/oom_kill.c > > > > > +++ b/mm/oom_kill.c > > > > > @@ -992,6 +992,13 @@ bool out_of_memory(struct oom_control *oc) > > > > > if (oom_killer_disabled) > > > > > return false; > > > > > > > > > > + /* > > > > > + * If there are oom victims in flight, we don't need to select > > > > > + * a new victim. > > > > > + */ > > > > > + if (atomic_read(&oom_victims) > 0) > > > > > + return true; > > > > > + > > > > > if (!is_memcg_oom(oc)) { > > > > > blocking_notifier_call_chain(&oom_notify_list, 0, &freed); > > > > > if (freed > 0) > > > > > > > > The OOM reaper is not available for CONFIG_MMU=n kernels, and timeout based > > > > giveup is not permitted, but a multithreaded process might be selected as > > > > an OOM victim. Not setting TIF_MEMDIE to all threads sharing an OOM victim's > > > > mm increases possibility of preventing some OOM victim thread from terminating > > > > (e.g. one of them cannot leave __alloc_pages_slowpath() with mmap_sem held for > > > > write due to waiting for the TIF_MEMDIE thread to call exit_oom_victim() when > > > > the TIF_MEMDIE thread is waiting for the thread with mmap_sem held for write). > > > > > > I agree, that CONFIG_MMU=n is a special case, and the proposed approach can't > > > be used directly. But can you, please, why do you find the first chunk wrong? > > > > Since you are checking oom_victims before checking task_will_free_mem(current), > > only one thread can get TIF_MEMDIE. This is where a multithreaded OOM victim without > > the OOM reaper can get stuck forever. > > Oops, I misinterpreted. This is where a multithreaded OOM victim with or without > the OOM reaper can get stuck forever. Think about a process with two threads is > selected by the OOM killer and only one of these two threads can get TIF_MEMDIE. > > Thread-1 Thread-2 The OOM killer The OOM reaper > > Calls down_write(¤t->mm->mmap_sem). > Enters __alloc_pages_slowpath(). > Enters __alloc_pages_slowpath(). > Takes oom_lock. > Calls out_of_memory(). > Selects Thread-1 as an OOM victim. > Gets SIGKILL. Gets SIGKILL. > Gets TIF_MEMDIE. > Releases oom_lock. > Leaves __alloc_pages_slowpath() because Thread-1 has TIF_MEMDIE. > Takes oom_lock. > Will do nothing because down_read_trylock() fails. > Releases oom_lock. > Gives up and sets MMF_OOM_SKIP after one second. > Takes oom_lock. > Calls out_of_memory(). > Will not check MMF_OOM_SKIP because Thread-1 still has TIF_MEMDIE. // <= get stuck waiting for Thread-1. > Releases oom_lock. > Will not leave __alloc_pages_slowpath() because Thread-2 does not have TIF_MEMDIE. > Will not call up_write(¤t->mm->mmap_sem). > Reaches do_exit(). > Calls down_read(¤t->mm->mmap_sem) in exit_mm() in do_exit(). // <= get stuck waiting for Thread-2. > Will not call up_read(¤t->mm->mmap_sem) in exit_mm() in do_exit(). > Will not clear TIF_MEMDIE in exit_oom_victim() in exit_mm() in do_exit(). That's interesting... Does it mean, that we have to give an access to the reserves to all threads to guarantee the forward progress? What do you think about Michal's approach? He posted a link in the thread. Thank you! Roman -- 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