From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754853AbbE1VHy (ORCPT ); Thu, 28 May 2015 17:07:54 -0400 Received: from mail-qg0-f46.google.com ([209.85.192.46]:33382 "EHLO mail-qg0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751812AbbE1VHr (ORCPT ); Thu, 28 May 2015 17:07:47 -0400 Date: Thu, 28 May 2015 17:07:42 -0400 From: Tejun Heo To: Johannes Weiner Cc: Michal Hocko , linux-mm@kvack.org, Oleg Nesterov , Vladimir Davydov , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Andrew Morton , LKML Subject: Re: [RFC 3/3] memcg: get rid of mm_struct::owner Message-ID: <20150528210742.GF27479@htj.duckdns.org> References: <1432641006-8025-1-git-send-email-mhocko@suse.cz> <1432641006-8025-4-git-send-email-mhocko@suse.cz> <20150526141011.GA11065@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150526141011.GA11065@cmpxchg.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Johannes, Michal. On Tue, May 26, 2015 at 10:10:11AM -0400, Johannes Weiner wrote: > On Tue, May 26, 2015 at 01:50:06PM +0200, Michal Hocko wrote: > > Please note that this patch introduces a USER VISIBLE CHANGE OF BEHAVIOR. > > Without mm->owner _all_ tasks associated with the mm_struct would > > initiate memcg migration while previously only owner of the mm_struct > > could do that. The original behavior was awkward though because the user > > task didn't have any means to find out the current owner (esp. after > > mm_update_next_owner) so the migration behavior was not well defined > > in general. > > New cgroup API (unified hierarchy) will discontinue tasks file which > > means that migrating threads will no longer be possible. In such a case > > having CLONE_VM without CLONE_THREAD could emulate the thread behavior > > but this patch prevents from isolating memcg controllers from others. > > Nevertheless I am not convinced such a use case would really deserve > > complications on the memcg code side. > > I think such a change is okay. The memcg semantics of moving threads > with the same mm into separate groups have always been arbitrary. No > reasonable behavior can be expected of this, so what sane real life > usecase would rely on it? I suppose that making mm always follow the threadgroup leader should be fine, right? While this wouldn't make any difference in the unified hierarchy, I think this would make more sense for traditional hierarchies. Thanks. -- tejun