From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx109.postini.com [74.125.245.109]) by kanga.kvack.org (Postfix) with SMTP id 3EC306B0093 for ; Sun, 14 Jul 2013 23:09:34 -0400 (EDT) Message-ID: <51E36788.6080308@huawei.com> Date: Mon, 15 Jul 2013 11:07:52 +0800 From: Li Zefan MIME-Version: 1.0 Subject: Re: [PATCH v2] vmpressure: make sure memcg stays alive until all users are signaled References: <20130711092542.GD21667@dhcp22.suse.cz> <51DE7AAF.6070004@huawei.com> <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> In-Reply-To: <20130712103731.GB15307@dhcp22.suse.cz> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Tejun Heo , Anton Vorontsov , cgroups@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , KAMEZAWA Hiroyuki , KOSAKI Motohiro 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. -- 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