From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f54.google.com (mail-wg0-f54.google.com [74.125.82.54]) by kanga.kvack.org (Postfix) with ESMTP id C0BFA6B0189 for ; Thu, 21 May 2015 13:22:41 -0400 (EDT) Received: by wgfl8 with SMTP id l8so92575713wgf.2 for ; Thu, 21 May 2015 10:22:41 -0700 (PDT) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id he9si36369551wjc.173.2015.05.21.10.22.38 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 21 May 2015 10:22:39 -0700 (PDT) Date: Thu, 21 May 2015 13:22:17 -0400 From: Johannes Weiner Subject: Re: [PATCH 3/7] memcg: immigrate charges only when a threadgroup leader is moved Message-ID: <20150521172217.GB12800@cmpxchg.org> References: <1431978595-12176-1-git-send-email-tj@kernel.org> <1431978595-12176-4-git-send-email-tj@kernel.org> <20150519121321.GB6203@dhcp22.suse.cz> <20150519212754.GO24861@htj.duckdns.org> <20150520131044.GA28678@dhcp22.suse.cz> <20150520132158.GB28678@dhcp22.suse.cz> <20150520175302.GA7287@redhat.com> <20150520202221.GD14256@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150520202221.GD14256@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Oleg Nesterov , Tejun Heo , lizefan@huawei.com, cgroups@vger.kernel.org, linux-mm@kvack.org On Wed, May 20, 2015 at 10:22:21PM +0200, Michal Hocko wrote: > On Wed 20-05-15 19:53:02, Oleg Nesterov wrote: > > On 05/20, Michal Hocko wrote: > > > > > > So I assume the leader simply waits for its threads to finish and it > > > stays in the sibling list. __unhash_process seems like it does the final > > > cleanup and unlinks the leader from the lists. Which means that > > > mm_update_next_owner never sees !group_leader. Is that correct Oleg? > > > > Yes, yes, the group leader can't go away until the whole thread-group dies. > > OK, then we should have a guarantee that mm->owner is always thread > group leader, right? > > > But can't we kill mm->owner somehow? > > I would be happy about that. But it is not that simple. > > > I mean, turn it into something else, > > ideally into "struct mem_cgroup *" although I doubt this is possible. > > Sounds like a good idea but... it duplicates the cgroup tracking into > two places and that asks for troubles. On the other hand we are doing > that already because mm->owner might be in a different cgroup than the > current. However, this is an inherent problem because CLONE_VM doesn't > imply CLONE_THREAD. So in the end it doesn't look much worse IMO. > We will loose the "this task is in charge" aspect and that would > be a user space visible change but I am not sure how much it is a > problem. Maybe somebody is (ab)using this to workaround the restriction > that all threads are in the same cgroup. If mm->owner is currently always the threadgroup leader, it should be fairly straight forward to maintain mm->memcg on all events that move any threadgroup leader between cgroups, without having mm->owner, no? It would have a lot of benefits for sure. The code would be simpler, but it would also reduce some of the cost that Mel is observing inside __mem_cgroup_count_vm_event(), by reducing one level of indirection. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org