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[37.188.254.25]) by smtp.gmail.com with ESMTPSA id p8sm24718070wrw.19.2020.03.16.02.32.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Mar 2020 02:32:38 -0700 (PDT) Date: Mon, 16 Mar 2020 10:32:36 +0100 From: Michal Hocko To: David Rientjes Cc: Andrew Morton , Vlastimil Babka , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch] mm, oom: prevent soft lockup on memcg oom for UP systems Message-ID: <20200316093236.GF11482@dhcp22.suse.cz> References: <20200310221019.GE8447@dhcp22.suse.cz> <20200311082736.GA23944@dhcp22.suse.cz> <20200312083241.GT23944@dhcp22.suse.cz> <20200312201624.GD23944@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200312201624.GD23944@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 12-03-20 21:16:27, Michal Hocko wrote: > On Thu 12-03-20 11:20:33, David Rientjes wrote: > > On Thu, 12 Mar 2020, Michal Hocko wrote: > > > > > > I think the changelog clearly states that we need to guarantee that a > > > > reclaimer will yield the processor back to allow a victim to exit. This > > > > is where we make the guarantee. If it helps for the specific reason it > > > > triggered in my testing, we could add: > > > > > > > > "For example, mem_cgroup_protected() can prohibit reclaim and thus any > > > > yielding in page reclaim would not address the issue." > > > > > > I would suggest something like the following: > > > " > > > The reclaim path (including the OOM) relies on explicit scheduling > > > points to hand over execution to tasks which could help with the reclaim > > > process. > > > > Are there other examples where yielding in the reclaim path would "help > > with the reclaim process" other than oom victims? This sentence seems > > vague. > > In the context of UP and !PREEMPT this also includes IO flushers, > filesystems rely on workers and there are things I am very likely not > aware of. If you think this is vaague then feel free to reformulate. > All I really do care about is what the next paragraph is explaining. Btw. do you plan to send a patch with an updated changelog? > > > Currently it is mostly shrink_page_list which yields CPU for > > > each reclaimed page. This might be insuficient though in some > > > configurations. E.g. when a memcg OOM path is triggered in a hierarchy > > > which doesn't have any reclaimable memory because of memory reclaim > > > protection (MEMCG_PROT_MIN) then there is possible to trigger a soft > > > lockup during an out of memory situation on non preemptible kernels > > > > > > > > > Fix this by adding a cond_resched up in the reclaim path and make sure > > > there is a yield point regardless of reclaimability of the target > > > hierarchy. > > > " > > > > > -- > Michal Hocko > SUSE Labs -- Michal Hocko SUSE Labs