Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754491AbaDPEWW (ORCPT ); Wed, 16 Apr 2014 00:22:22 -0400 Received: from szxga02-in.huawei.com ([119.145.14.65]:39724 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751361AbaDPEWS (ORCPT ); Wed, 16 Apr 2014 00:22:18 -0400 Message-ID: <534E04F1.4070104@huawei.com> Date: Wed, 16 Apr 2014 12:20:01 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: "Eric W. Biederman" CC: Kay Sievers , , Greg Kroah-Hartman , , , LKML , "Lennart Poettering" , , Tejun Heo , , Subject: Re: [PATCH 3/3] cgroup: implement cgroup.subtree_populated for the default hierarchy References: <1397511846-2904-1-git-send-email-tj@kernel.org> <1397511846-2904-4-git-send-email-tj@kernel.org> <534DEF62.4090900@huawei.com> <87tx9uhr0j.fsf@x220.int.ebiederm.org> In-Reply-To: <87tx9uhr0j.fsf@x220.int.ebiederm.org> Content-Type: text/plain; charset="GB2312" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.18.230] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014/4/16 11:50, Eric W. Biederman wrote: > Kay Sievers writes: > >> On Tue, Apr 15, 2014 at 7:48 PM, Li Zefan wrote: >>> On 2014/4/15 5:44, Tejun Heo wrote: >>>> cgroup users often need a way to determine when a cgroup's >>>> subhierarchy becomes empty so that it can be cleaned up. cgroup >>>> currently provides release_agent for it; unfortunately, this mechanism >>>> is riddled with issues. >>>> >>>> * It delivers events by forking and execing a userland binary >>>> specified as the release_agent. This is a long deprecated method of >>>> notification delivery. It's extremely heavy, slow and cumbersome to >>>> integrate with larger infrastructure. >>>> >>>> * There is single monitoring point at the root. There's no way to >>>> delegate management of subtree. >>>> >>>> * The event isn't recursive. It triggers when a cgroup doesn't have >>>> any tasks or child cgroups. Events for internal nodes trigger only >>>> after all children are removed. This again makes it impossible to >>>> delegate management of subtree. >>>> >>>> * Events are filtered from the kernel side. "notify_on_release" file >>>> is used to subscribe to or suppress release event. This is >>>> unnecessarily complicated and probably done this way because event >>>> delivery itself was expensive. >>>> >>>> This patch implements interface file "cgroup.subtree_populated" which >>>> can be used to monitor whether the cgroup's subhierarchy has tasks in >>>> it or not. Its value is 0 if there is no task in the cgroup and its >>>> descendants; otherwise, 1, and kernfs_notify() notificaiton is >>>> triggers when the value changes, which can be monitored through poll >>>> and [di]notify. >>>> >>> >>> For the old notification mechanism, the path of the cgroup that becomes >>> empty will be passed to the user specified release agent. Like this: >>> >>> # cat /sbin/cpuset_release_agent >>> #!/bin/sh >>> rmdir /dev/cpuset/$1 >>> >>> How do we achieve this using inotify? >>> >>> - monitor all the cgroups, or >>> - monitor all the leaf cgroups, and travel cgrp->parent to delete all >>> empty cgroups. >>> - monitor root cgroup only, and travel the whole hierarchy to find >>> empy cgroups when it gets an fs event. >>> >>> Seems none of them is scalible. >> >> The manager would add all cgroups as watches to one inotify file >> descriptor, it should not be problem to do that. > > inotify won't work on cgroupfs. > Tejun's working on inotify support for cgroupfs, and I believe this patchset has been tested, so it works. So what do you mean by saying it won't work? Could you be more specific? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/