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[202.181.97.72]) by mx.google.com with ESMTPS id u21si12593405pgm.431.2019.07.02.06.19.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 02 Jul 2019 06:19:44 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of penguin-kernel@i-love.sakura.ne.jp designates 202.181.97.72 as permitted sender) client-ip=202.181.97.72; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of penguin-kernel@i-love.sakura.ne.jp designates 202.181.97.72 as permitted sender) smtp.mailfrom=penguin-kernel@i-love.sakura.ne.jp Received: from fsav303.sakura.ne.jp (fsav303.sakura.ne.jp [153.120.85.134]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x62DJanh095690; Tue, 2 Jul 2019 22:19:37 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav303.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav303.sakura.ne.jp); Tue, 02 Jul 2019 22:19:36 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav303.sakura.ne.jp) Received: from [192.168.1.8] (softbank126012062002.bbtec.net [126.12.62.2]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id x62DJV3T095658 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Tue, 2 Jul 2019 22:19:36 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] mm: mempolicy: don't select exited threads as OOM victims To: Michal Hocko Cc: Shakeel Butt , linux-mm@kvack.org References: <1561807474-10317-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20190701111708.GP6376@dhcp22.suse.cz> <15099126-5d0f-51eb-7134-46c5c2db3bf0@i-love.sakura.ne.jp> <20190701131736.GX6376@dhcp22.suse.cz> <20190701134859.GZ6376@dhcp22.suse.cz> <20190701140434.GA6376@dhcp22.suse.cz> <20190701141647.GB6376@dhcp22.suse.cz> From: Tetsuo Handa Message-ID: <0d81f46e-0b5f-0792-637f-fa88468f33cf@i-love.sakura.ne.jp> Date: Tue, 2 Jul 2019 22:19:27 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190701141647.GB6376@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2019/07/01 23:16, Michal Hocko wrote: > Thinking about it some more it seems that we can go with your original > fix if we also reorder oom_evaluate_task > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index f719b64741d6..e5feb0f72e3b 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -318,9 +318,6 @@ static int oom_evaluate_task(struct task_struct *task, void *arg) > struct oom_control *oc = arg; > unsigned long points; > > - if (oom_unkillable_task(task, NULL, oc->nodemask)) > - goto next; > - > /* > * This task already has access to memory reserves and is being killed. > * Don't allow any other task to have access to the reserves unless > @@ -333,6 +330,9 @@ static int oom_evaluate_task(struct task_struct *task, void *arg) > goto abort; > } > > + if (oom_unkillable_task(task, NULL, oc->nodemask)) > + goto next; > + > /* > * If task is allocating a lot of memory and has been marked to be > * killed first if it triggers an oom, then select it. > > I do not see any strong reason to keep the current ordering. OOM victim > check is trivial so it shouldn't add a visible overhead for few > unkillable tasks that we might encounter. > Yes if we can tolerate that there can be only one OOM victim for !memcg OOM events (because an OOM victim in a different OOM context will hit "goto abort;" path). Thinking again, I think that the same problem exists for mask == NULL path as long as "a process with dying leader and live threads" is possible. Then, fixing up after has_intersects_mems_allowed()/cpuset_mems_allowed_intersects() judged that some thread is eligible is better. diff --git a/mm/oom_kill.c b/mm/oom_kill.c index d1c9c4e..43e499e 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -109,8 +109,23 @@ static bool oom_cpuset_eligible(struct task_struct *start, */ ret = cpuset_mems_allowed_intersects(current, tsk); } - if (ret) - break; + if (ret) { + /* + * Exclude dead threads as ineligible when selecting + * an OOM victim. But include dead threads as eligible + * when waiting for OOM victims to get MMF_OOM_SKIP. + * + * Strictly speaking, tsk->mm should be checked under + * task lock because cpuset_mems_allowed_intersects() + * does not take task lock. But racing with exit_mm() + * is not fatal. Thus, use cheaper barrier rather than + * strict task lock. + */ + smp_rmb(); + if (tsk->mm || tsk_is_oom_victim(tsk)) + break; + ret = false; + } } rcu_read_unlock();