From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Gushchin Subject: Re: [v6 2/4] mm, oom: cgroup-aware OOM killer Date: Thu, 24 Aug 2017 14:58:42 +0100 Message-ID: <20170824135842.GA21167@castle.DHCP.thefacebook.com> References: <20170823165201.24086-1-guro@fb.com> <20170823165201.24086-3-guro@fb.com> <20170824114706.GG5943@dhcp22.suse.cz> <20170824122846.GA15916@castle.DHCP.thefacebook.com> <20170824125811.GK5943@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=facebook; bh=Vp0LA3RM9z4yREQ9fG6CH8tyP7LBA2f9IIkEI8xlt8I=; b=c6rE/R++0xdNxGEXdy4G7EGRc/E1KnhKfjDG0+kEHpkOuG5IADDXxXyRpW+dwzSK2CZm syai23uyD/NpXEI80CbWM7MlV5EdnC2GCe9V/waPBIXdeqdonfCvaNpEgUjJhaokVqOJ 9uLh6Qsf+lDAxd26jpphe8NKlV9+QMH3y70= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.onmicrosoft.com; s=selector1-fb-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version; bh=Vp0LA3RM9z4yREQ9fG6CH8tyP7LBA2f9IIkEI8xlt8I=; b=RlmKo4HlGpG4JbW6hjlkWcYqA8tJRILGtQR8F95odrvVz4DlzD0Zy/z4MfgCi3idirQCgel6+CBGkwI2AKjRh2JYHFNvCeYT97V6U+mcs7DORmBVh8sykltLiqTbKMYmHfIQ+UkN1QILfZN3Yz5CHHWSga2GViSBxwyH1ynSLrs= Content-Disposition: inline In-Reply-To: <20170824125811.GK5943-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Transfer-Encoding: 7bit To: Michal Hocko Cc: linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Vladimir Davydov , Johannes Weiner , Tetsuo Handa , David Rientjes , Tejun Heo , kernel-team-b10kYP2dOMg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Thu, Aug 24, 2017 at 02:58:11PM +0200, Michal Hocko wrote: > On Thu 24-08-17 13:28:46, Roman Gushchin wrote: > > Hi Michal! > > > There is nothing like a "better victim". We are pretty much in a > catastrophic situation when we try to survive by killing a userspace. Not necessary, it can be a cgroup OOM. > We try to kill the largest because that assumes that we return the > most memory from it. Now I do understand that you want to treat the > memcg as a single killable entity but I find it really questionable > to do a per-memcg metric and then do not treat it like that and kill > only a single task. Just imagine a single memcg with zillions of taks > each very small and you select it as the largest while a small taks > itself doesn't help to help to get us out of the OOM. I don't think it's different from a non-containerized state: if you have a zillion of small tasks in the system, you'll meet the same issues. > > > I guess I have asked already and we haven't reached any consensus. I do > > > not like how you treat memcgs and tasks differently. Why cannot we have > > > a memcg score a sum of all its tasks? > > > > It sounds like a more expensive way to get almost the same with less accuracy. > > Why it's better? > > because then you are comparing apples to apples? Well, I can say that I compare some number of pages against some other number of pages. And the relation between a page and memcg is more obvious, than a relation between a page and a process. Both ways are not ideal, and sum of the processes is not ideal too. Especially, if you take oom_score_adj into account. Will you respect it? I've started actually with such approach, but then found it weird. > Besides that you have > to check each task for over-killing anyway. So I do not see any > performance merits here. It's an implementation detail, and we can hopefully get rid of it at some point. > > > > How do you want to compare memcg score with tasks score? > > > > I have to do it for tasks in root cgroups, but it shouldn't be a common case. > > How come? I can easily imagine a setup where only some memcgs which > really do need a kill-all semantic while all others can live with single > task killed perfectly fine. I mean taking a unified cgroup hierarchy into an account, there should not be lot of tasks in the root cgroup, if any.