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[37.188.183.9]) by smtp.gmail.com with ESMTPSA id o3sm1639526wru.68.2020.05.05.00.29.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 May 2020 00:29:32 -0700 (PDT) Date: Tue, 5 May 2020 09:29:31 +0200 From: Michal Hocko To: Andrew Morton Cc: Yafang Shao , linux-mm@kvack.org, Chris Down , Johannes Weiner Subject: Re: [PATCH resend] mm, memcg: fix inconsistent oom event behavior Message-ID: <20200505072931.GE16322@dhcp22.suse.cz> References: <20200502141055.7378-1-laoar.shao@gmail.com> <20200504160345.45801b7bf199ac5897e2572a@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200504160345.45801b7bf199ac5897e2572a@linux-foundation.org> 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 Mon 04-05-20 16:03:45, Andrew Morton wrote: > On Sat, 2 May 2020 10:10:55 -0400 Yafang Shao wrote: > > > A recent commit 9852ae3fe529 ("mm, memcg: consider subtrees in > > memory.events") changes the behavior of memcg events, which will > > consider subtrees in memory.events. But oom_kill event is a special one > > as it is used in both cgroup1 and cgroup2. In cgroup1, it is displayed > > in memory.oom_control. The file memory.oom_control is in both root memcg > > and non root memcg, that is different with memory.event as it only in > > non-root memcg. That commit is okay for cgroup2, but it is not okay for > > cgroup1 as it will cause inconsistent behavior between root memcg and > > non-root memcg. > > > > Here's an example on why this behavior is inconsistent in cgroup1. > > root memcg > > / > > memcg foo > > / > > memcg bar > > > > Suppose there's an oom_kill in memcg bar, then the oon_kill will be > > > > root memcg : memory.oom_control(oom_kill) 0 > > / > > memcg foo : memory.oom_control(oom_kill) 1 > > / > > memcg bar : memory.oom_control(oom_kill) 1 > > > > For the non-root memcg, its memory.oom_control(oom_kill) includes its > > descendants' oom_kill, but for root memcg, it doesn't include its > > descendants' oom_kill. That means, memory.oom_control(oom_kill) has > > different meanings in different memcgs. That is inconsistent. Then the user > > has to know whether the memcg is root or not. > > > > If we can't fully support it in cgroup1, for example by adding > > memory.events.local into cgroup1 as well, then let's don't touch > > its original behavior. > > > > Fixes: 9852ae3fe529 ("mm, memcg: consider subtrees in memory.events") > > Nearly a year ago. Should we backport this into earlier kernels? It is a trivial change so I do not see problem marking it for stable. > > > --- a/include/linux/memcontrol.h > > +++ b/include/linux/memcontrol.h > > @@ -783,6 +783,8 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg, > > atomic_long_inc(&memcg->memory_events[event]); > > cgroup_file_notify(&memcg->events_file); > > > > + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) > > + break; > > if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS) > > break; > > } while ((memcg = parent_mem_cgroup(memcg)) && -- Michal Hocko SUSE Labs