From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx181.postini.com [74.125.245.181]) by kanga.kvack.org (Postfix) with SMTP id 86DAE6B00A7 for ; Mon, 15 Jul 2013 05:20:35 -0400 (EDT) Date: Mon, 15 Jul 2013 11:20:33 +0200 From: Michal Hocko Subject: Re: [PATCH v2] vmpressure: make sure memcg stays alive until all users are signaled Message-ID: <20130715092033.GB26199@dhcp22.suse.cz> References: <20130711093300.GE21667@dhcp22.suse.cz> <20130711154408.GA9229@mtj.dyndns.org> <20130711162215.GM21667@dhcp22.suse.cz> <20130711163238.GC9229@mtj.dyndns.org> <20130712084039.GA13224@dhcp22.suse.cz> <51DFCA49.4080407@huawei.com> <20130712092927.GA15307@dhcp22.suse.cz> <51DFD253.3030501@huawei.com> <20130712103731.GB15307@dhcp22.suse.cz> <51E36788.6080308@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51E36788.6080308@huawei.com> Sender: owner-linux-mm@kvack.org List-ID: To: Li Zefan Cc: Tejun Heo , Anton Vorontsov , cgroups@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , KAMEZAWA Hiroyuki , KOSAKI Motohiro On Mon 15-07-13 11:07:52, Li Zefan wrote: > On 2013/7/12 18:37, Michal Hocko wrote: > > On Fri 12-07-13 17:54:27, Li Zefan wrote: > >> On 2013/7/12 17:29, Michal Hocko wrote: > >>> On Fri 12-07-13 17:20:09, Li Zefan wrote: > >>> [...] > >>>> But if I read the code correctly, even no one registers a vmpressure event, > >>>> vmpressure() is always running and queue the work item. > >>> > >>> True but checking there is somebody is rather impractical. First we > >>> would have to take a events_lock to check this and then drop it after > >>> scheduling the work. Which doesn't guarantee that the registered event > >>> wouldn't go away. > >>> And even trickier, we would have to do the same for all parents up the > >>> hierarchy. > >>> > >> > >> The thing is, we can forget about eventfd. eventfd is checked in > >> vmpressure_work_fn(), while vmpressure() is always called no matter what. > > > > But vmpressure is called only for an existing memcg. This means that > > it cannot be called past css_offline so it must happen _before_ cgroup > > eventfd cleanup code. > > > > Or am I missing something? > > > > Yeah. > > The vmpressure work item is queued if we sense some memory pressure, no matter > if there is any eventfd ever registered. This is the point. But it is queued on vmpr which is embedded in the memcg which is the _target_ of the reclaim. There is _no reclaim_ for a memcg after css has been deactivated which happens _before_ css_offline. /me confused. -- 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