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Wed, 11 Mar 2020 15:14:41 -0700 (PDT) Received: from [2620:15c:17:3:3a5:23a7:5e32:4598] ([2620:15c:17:3:3a5:23a7:5e32:4598]) by smtp.gmail.com with ESMTPSA id a143sm29357820pfd.108.2020.03.11.15.14.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Mar 2020 15:14:40 -0700 (PDT) Date: Wed, 11 Mar 2020 15:14:39 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Tetsuo Handa cc: Andrew Morton , Vlastimil Babka , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch] mm, oom: prevent soft lockup on memcg oom for UP systems In-Reply-To: <993e7783-60e9-ba03-b512-c829b9e833fd@i-love.sakura.ne.jp> Message-ID: References: <0e5ca6ee-d460-db8e-aba2-79aa7a66fad1@I-love.SAKURA.ne.jp> <7a6170fc-b247-e327-321a-b99fb53f552d@i-love.sakura.ne.jp> <993e7783-60e9-ba03-b512-c829b9e833fd@i-love.sakura.ne.jp> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Bogosity: Ham, tests=bogofilter, spamicity=0.000693, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 12 Mar 2020, Tetsuo Handa wrote: > > The cond_resched() here is needed if the iteration is lengthy depending on > > the number of descendant memcgs already. > > No. cond_resched() here will become no-op if CONFIG_PREEMPTION=y and current > thread has realtime priority. > It's helpful without CONFIG_PREEMPTION for excessively long memcg iterations to avoid starving need_resched. > > schedule_timeout_killable(1) does not make any guarantees that current > > will be scheduled after the victim or oom_reaper on UP systems. > > The point of schedule_timeout_*(1) is to guarantee that current thread > will yield CPU to other threads even if CONFIG_PREEMPTION=y and current > thread has realtime priority case. There is no guarantee that current > thread will be rescheduled immediately after a sleep is irrelevant. > > > > > If you have an alternate patch to try, we can test it. But since this > > cond_resched() is needed anyway, I'm not sure it will change the result. > > schedule_timeout_killable(1) is an alternate patch to try; I don't think > that this cond_resched() is needed anyway. > You are suggesting schedule_timeout_killable(1) in shrink_node_memcgs()?