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[213.151.95.130]) by smtp.gmail.com with ESMTPSA id y19sm7673034wmd.29.2019.11.25.00.20.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Nov 2019 00:20:40 -0800 (PST) Date: Mon, 25 Nov 2019 09:20:40 +0100 From: Michal Hocko To: Yafang Shao Cc: Johannes Weiner , Vladimir Davydov , Andrew Morton , Linux MM Subject: Re: [PATCH] mm, memcg: show memcg min setting in oom messages Message-ID: <20191125082040.GB31714@dhcp22.suse.cz> References: <1574239985-1916-1-git-send-email-laoar.shao@gmail.com> <20191120102157.GF23213@dhcp22.suse.cz> <20191120114043.GH23213@dhcp22.suse.cz> <20191122102842.GR23213@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) 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 Sat 23-11-19 13:52:57, Yafang Shao wrote: > On Fri, Nov 22, 2019 at 6:28 PM Michal Hocko wrote: > > > > On Wed 20-11-19 20:23:54, Yafang Shao wrote: > > > On Wed, Nov 20, 2019 at 7:40 PM Michal Hocko wrote: > > > > > > > > On Wed 20-11-19 18:53:44, Yafang Shao wrote: > > > > > On Wed, Nov 20, 2019 at 6:22 PM Michal Hocko wrote: > > > > > > > > > > > > On Wed 20-11-19 03:53:05, Yafang Shao wrote: > > > > > > > A task running in a memcg may OOM because of the memory.min settings of his > > > > > > > slibing and parent. If this happens, the current oom messages can't show > > > > > > > why file page cache can't be reclaimed. > > > > > > > > > > > > min limit is not the only way to protect memory from being reclaim. The > > > > > > memory might be pinned or unreclaimable for other reasons (e.g. swap > > > > > > quota exceeded for memcg). > > > > > > > > > > Both swap or unreclaimabed (unevicteable) is printed in OOM messages. > > > > > > > > Not really. Consider a memcg which has reached it's swap limit. The > > > > anonymous memory is not really reclaimable even when there is a lot of > > > > swap space available. > > > > > > > > > > The memcg swap limit is already printed in oom messages, see bellow, > > > > > > [ 141.721625] memory: usage 1228800kB, limit 1228800kB, failcnt 18337 > > > [ 141.721958] swap: usage 0kB, limit 9007199254740988kB, failcnt 0 > > > > But you do not have any insight on the swap limit down the oom > > hierarchy, do you? > > > > > > > Why not just print the memcgs which are under memory.min protection or > > > > > something like a total number of min protected memory ? > > > > > > > > Yes, this would likely help. But the main question really reamains, is > > > > this really worth it? > > > > > > > > > > If it doesn't cost too much, I think it is worth to do it. > > > As the oom path is not the critical path, so adding some print info > > > should not add much overhead. > > > > Generating a lot of output for the oom reports has been a real problem > > in many deployments. > > So why not only print non-zero counters ? > If some counters are 0, we don't print them, that can reduce the oom reports. > > Something like "isolated_file:0 unevictable:0 dirty:0 writeback:0 > unstable:0" can all be removed, > and we consider them as zero by default. because that would make parsing more complex. > I mean we can optimze the OOM reports and only print the useful > information to make it not be a problem in many deployments. We can, but it would be great to have it backed by som real usecase to change the current behavior. I haven't heard anything so far. It is all about "this would be nice" without a strong justification. -- Michal Hocko SUSE Labs