Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752007AbaDPEPh (ORCPT ); Wed, 16 Apr 2014 00:15:37 -0400 Received: from mail-wg0-f46.google.com ([74.125.82.46]:55868 "EHLO mail-wg0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750919AbaDPEPd (ORCPT ); Wed, 16 Apr 2014 00:15:33 -0400 MIME-Version: 1.0 In-Reply-To: <87tx9uhr0j.fsf@x220.int.ebiederm.org> 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> From: Kay Sievers Date: Tue, 15 Apr 2014 21:15:10 -0700 Message-ID: Subject: Re: [PATCH 3/3] cgroup: implement cgroup.subtree_populated for the default hierarchy To: "Eric W. Biederman" Cc: Li Zefan , rlove@rlove.org, Greg Kroah-Hartman , containers@lists.linux-foundation.org, serge.hallyn@ubuntu.com, LKML , Lennart Poettering , eparis@parisplace.org, Tejun Heo , cgroups@vger.kernel.org, john@johnmccutchan.com Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 15, 2014 at 8:50 PM, 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. Inotify on kernfs will work. Kay -- 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/