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Sat, 02 May 2020 07:35:29 -0700 (PDT) Received: from localhost.localdomain ([203.100.54.194]) by smtp.gmail.com with ESMTPSA id o10sm4244867pgb.78.2020.05.02.07.35.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 02 May 2020 07:35:29 -0700 (PDT) From: Yafang Shao To: akpm@linux-foundation.org Cc: shakeelb@google.com, hannes@cmpxchg.org, mhocko@kernel.org, guro@fb.com, gthelen@google.com, linux-mm@kvack.org, Yafang Shao Subject: [PATCH 2/2] mm, memcg: don't try to kill a process if memcg is not populated Date: Sat, 2 May 2020 10:34:52 -0400 Message-Id: <20200502143452.7640-3-laoar.shao@gmail.com> X-Mailer: git-send-email 2.18.1 In-Reply-To: <20200502143452.7640-1-laoar.shao@gmail.com> References: <20200502143452.7640-1-laoar.shao@gmail.com> 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: Recently Shakeel reported a issue which also confused me serveral months earlier. Bellow is his report - Lowering memory.max can trigger an oom-kill if the reclaim does not succeed. However if oom-killer does not find a process for killing, it dumps a lot of warnings. Deleting a memcg does not reclaim memory from it and the memory can linger till there is a memory pressure. One normal way to proactively reclaim such memory is to set memory.max to 0 just before deleting the memcg. However if some of the memcg's memory is pinned by others, this operation can trigger an oom-kill without any process and thus can log a lot un-needed warnings. So, ignore all such warnings from memory.max. [shakeelb@google.com: commit log above] A better way to avoid this issue is to avoid trying to kill a process if memcg is not populated. Note that OOM is different with OOM kill. OOM is a status that the system or memcg is out of memory, while OOM kill is a result that a process inside this memcg is killed when this memcg is in OOM status. That is the same reason why there're both MEMCG_OOM event and MEMCG_OOM_KILL event. If we have already known that there's nothing to kill, i.e. the memcg is not populated, then we don't need to have a try. Cc: Shakeel Butt Cc: Johannes Weiner Cc: Michal Hocko Cc: Roman Gushchin Cc: Greg Thelen Signed-off-by: Yafang Shao Reviewed-by: Shakeel Butt --- mm/memcontrol.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 985edce98491..29afe3df9d98 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6102,6 +6102,10 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, } memcg_memory_event(memcg, MEMCG_OOM); + + if (!cgroup_is_populated(memcg->css.cgroup)) + break; + if (!mem_cgroup_oom_kill(memcg, GFP_KERNEL, 0)) break; }