From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx156.postini.com [74.125.245.156]) by kanga.kvack.org (Postfix) with SMTP id 0670E6B0005 for ; Thu, 4 Apr 2013 11:20:31 -0400 (EDT) Date: Thu, 4 Apr 2013 17:20:28 +0200 From: Michal Hocko Subject: Re: [RFC][PATCH 5/7] cgroup: make sure parent won't be destroyed before its children Message-ID: <20130404152028.GK29911@dhcp22.suse.cz> References: <515BF233.6070308@huawei.com> <515BF2A4.1070703@huawei.com> <20130404113750.GH29911@dhcp22.suse.cz> <20130404133706.GA9425@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130404133706.GA9425@htj.dyndns.org> Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: Li Zefan , linux-mm@kvack.org, LKML , Cgroups , Glauber Costa , KAMEZAWA Hiroyuki , Johannes Weiner On Thu 04-04-13 06:53:53, Tejun Heo wrote: > Hey, > > On Thu, Apr 04, 2013 at 01:37:50PM +0200, Michal Hocko wrote: > > On Wed 03-04-13 17:13:08, Li Zefan wrote: > > > Suppose we rmdir a cgroup and there're still css refs, this cgroup won't > > > be freed. Then we rmdir the parent cgroup, and the parent is freed due > > > to css ref draining to 0. Now it would be a disaster if the child cgroup > > > tries to access its parent. > > > > Hmm, I am not sure what is the correct layer for this to handle - cgroup > > core or memcg. But we have enforced that in mem_cgroup_css_online where > > we take an additional reference to the memcg. > > > > Handling it in the memcg code would have an advantage of limiting an > > additional reference only to use_hierarchy cases which is sufficient > > as we never touch the parent otherwise (parent_mem_cgroup). > > But what harm does an additional reference do? No harm at all. I just wanted to be sure that this is not yet another "for memcg" hack. So if this is useful for other controllers then I have no objections of course. > And given that there are cgroup core interfaces which access ->parent, > I think it'd be a good idea that parent always exists while there are > children. > > Thanks. -- 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