From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx135.postini.com [74.125.245.135]) by kanga.kvack.org (Postfix) with SMTP id 0E82D6B0032 for ; Fri, 12 Jul 2013 05:55:48 -0400 (EDT) Message-ID: <51DFD253.3030501@huawei.com> Date: Fri, 12 Jul 2013 17:54:27 +0800 From: Li Zefan MIME-Version: 1.0 Subject: Re: [PATCH v2] vmpressure: make sure memcg stays alive until all users are signaled References: <20130711083110.GC21667@dhcp22.suse.cz> <51DE701C.6010800@huawei.com> <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> In-Reply-To: <20130712092927.GA15307@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 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. vmpressure() queue_work() cgroup_diput() call_rcu(cgroup_free_rcu) ... queue_work(destroy_cgroup) ... cgroup_free_fn() mem_cgroup_destroy() ... vmpress_work_fn() There's no guarantee that vmpressure work is run before cgroup destroy work, I think. -- 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