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[216.49.36.201]) by smtp.gmail.com with ESMTPSA id b83-v6sm12524909qkc.20.2018.08.01.10.45.18 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 01 Aug 2018 10:45:19 -0700 (PDT) Date: Wed, 1 Aug 2018 13:48:14 -0400 From: Johannes Weiner To: Michal Hocko Cc: Roman Gushchin , linux-mm@kvack.org, David Rientjes , Tetsuo Handa , Tejun Heo , kernel-team@fb.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] mm, oom: introduce memory.oom.group Message-ID: <20180801174814.GC11386@cmpxchg.org> References: <20180730180100.25079-1-guro@fb.com> <20180730180100.25079-4-guro@fb.com> <20180731090700.GF4557@dhcp22.suse.cz> <20180801011447.GB25953@castle.DHCP.thefacebook.com> <20180801055503.GB16767@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180801055503.GB16767@dhcp22.suse.cz> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 01, 2018 at 07:55:03AM +0200, Michal Hocko wrote: > On Tue 31-07-18 18:14:48, Roman Gushchin wrote: > > On Tue, Jul 31, 2018 at 11:07:00AM +0200, Michal Hocko wrote: > > > On Mon 30-07-18 11:01:00, Roman Gushchin wrote: > > > > +struct mem_cgroup *mem_cgroup_get_oom_group(struct task_struct *victim, > > > > + struct mem_cgroup *oom_domain) > > > > +{ > > > > + struct mem_cgroup *oom_group = NULL; > > > > + struct mem_cgroup *memcg; > > > > + > > > > + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) > > > > + return NULL; > > > > + > > > > + if (!oom_domain) > > > > + oom_domain = root_mem_cgroup; > > > > + > > > > + rcu_read_lock(); > > > > + > > > > + memcg = mem_cgroup_from_task(victim); > > > > + if (!memcg || memcg == root_mem_cgroup) > > > > + goto out; > > > > > > When can we have memcg == NULL? victim should be always non-NULL. > > > Also why do you need to special case the root_mem_cgroup here. The loop > > > below should handle that just fine no? > > > > Idk, I prefer to keep an explicit root_mem_cgroup check, > > rather than traversing the tree and relying on an inability > > to set oom_group on the root. > > I will not insist but this just makes the code harder to read. Just FYI, I'd prefer the explicit check. The loop would do the right thing, but it's a little too implicit and subtle for my taste...