From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f181.google.com (mail-wi0-f181.google.com [209.85.212.181]) by kanga.kvack.org (Postfix) with ESMTP id E2D456B0142 for ; Wed, 20 May 2015 16:22:24 -0400 (EDT) Received: by wibt6 with SMTP id t6so72771862wib.0 for ; Wed, 20 May 2015 13:22:24 -0700 (PDT) Received: from mail-wg0-x235.google.com (mail-wg0-x235.google.com. [2a00:1450:400c:c00::235]) by mx.google.com with ESMTPS id o9si5826471wib.9.2015.05.20.13.22.22 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 20 May 2015 13:22:23 -0700 (PDT) Received: by wgfl8 with SMTP id l8so64692160wgf.2 for ; Wed, 20 May 2015 13:22:22 -0700 (PDT) Date: Wed, 20 May 2015 22:22:21 +0200 From: Michal Hocko Subject: Re: [PATCH 3/7] memcg: immigrate charges only when a threadgroup leader is moved Message-ID: <20150520202221.GD14256@dhcp22.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150520175302.GA7287@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Oleg Nesterov Cc: Tejun Heo , lizefan@huawei.com, cgroups@vger.kernel.org, hannes@cmpxchg.org, linux-mm@kvack.org 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. >>From the implementation POV it even looks easier because we just have to hook to fork (pin the memcg on dup_mm), to attach to change the memcg and to mmput to unpin the memcg. I will think about that some more. > It would be nice to kill mm_update_next_owner()/etc, this looks really > ugly. We only need it for mem_cgroup_from_task(), and it would be much > more clean to have mem_cgroup_from_mm(struct mm_struct *mm), imho. > > Oleg. > -- Michal Hocko SUSE Labs -- 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