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Mon, 16 Mar 2020 21:09:50 -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 c15sm1122631pja.30.2020.03.16.21.09.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Mar 2020 21:09:49 -0700 (PDT) Date: Mon, 16 Mar 2020 21:09:48 -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: <202003170318.02H3IpSx047471@www262.sakura.ne.jp> Message-ID: References: <8395df04-9b7a-0084-4bb5-e430efe18b97@i-love.sakura.ne.jp> <202003170318.02H3IpSx047471@www262.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=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 17 Mar 2020, Tetsuo Handa wrote: > > if (!fatal_signal_pending(current)) > > schedule_timeout_killable(1); > > > > So we don't have this reliance on all other memory chargers to yield when > > their charge fails and there is no delay for victims themselves. > > I see. You want below functions for environments where current thread can > fail to resume execution for long if current thread once reschedules (e.g. > UP kernel, many threads contended on one CPU). > > /* > * Give other threads CPU time, unless current thread was already killed. > * Used when we prefer killed threads to continue execution (in a hope that > * killed threads terminate quickly) over giving other threads CPU time. > */ > signed long __sched schedule_timeout_killable_expedited(signed long timeout) > { > if (unlikely(fatal_signal_pending(current))) > return timeout; > return schedule_timeout_killable(timeout); > } > I simply want the if (!fatal_signal_pending(current)) schedule_timeout_killable(1); after dropping oom_lock because I don't know that a generic function would be useful outside of this single place. If it becomes a regular pattern, for whatever reason, I think we can consider a new schedule_timeout variant. > /* > * Latency reduction via explicit rescheduling in places that are safe, > * but becomes no-op if current thread was already killed. Used when we > * prefer killed threads to continue execution (in a hope that killed > * threads terminate quickly) over giving other threads CPU time. > */ > int cond_resched_expedited(void) > { > if (unlikely(fatal_signal_pending(current))) > return 0; > return cond_resched(); > } > > > > > [ I'll still propose my change that adds cond_resched() to > > shrink_node_memcgs() because we can see need_resched set for a > > prolonged period of time without scheduling. ] > > As long as there is schedule_timeout_killable(), I'm fine with adding > cond_resched() in other places. > Sounds good, thanks Tetsuo.