From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx175.postini.com [74.125.245.175]) by kanga.kvack.org (Postfix) with SMTP id F0A9E6B0044 for ; Fri, 27 Jul 2012 02:18:09 -0400 (EDT) Message-ID: <501231F0.8050505@huawei.com> Date: Fri, 27 Jul 2012 14:15:12 +0800 From: Li Zefan MIME-Version: 1.0 Subject: Re: [PATCH] cgroup: Don't drop the cgroup_mutex in cgroup_rmdir References: <87ipdjc15j.fsf@skywalker.in.ibm.com> <1342706972-10912-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20120719165046.GO24336@google.com> <1342799140.2583.6.camel@twins> <20120720200542.GD21218@google.com> In-Reply-To: <20120720200542.GD21218@google.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: Peter Zijlstra , "Aneesh Kumar K.V" , akpm@linux-foundation.org, mhocko@suse.cz, kamezawa.hiroyu@jp.fujitsu.com, liwanp@linux.vnet.ibm.com, cgroups@vger.kernel.org, linux-mm@kvack.org, glommer@parallels.com On 2012/7/21 4:05, Tejun Heo wrote: > Hey, Peter. > > On Fri, Jul 20, 2012 at 05:45:40PM +0200, Peter Zijlstra wrote: >>> So, Peter, why does cpuset mangle with cgroup_mutex? What guarantees >>> does it need? Why can't it work on "changed" notification while >>> caching the current css like blkcg does? >> >> I've no clue sorry.. /me goes stare at this stuff.. Looks like something >> Paul Menage did when he created cgroups. I'll have to have a hard look >> at all that to untangle this. Not something obvious to me. > > Yeah, it would be great if this can be untangled. I really don't see > any other reasonable way out of this circular locking mess. If cpuset > needs stable css association across certain period, the RTTD is > caching the css by holding its ref and synchronize modifications to > that cache, rather than synchronizing cgroup operations themselves. > The cgroup core was extracted from cpuset, so they are deeply tangled. There are several issues to resolve with regard to removing cgroup lock from cpuset. - there are places that the cgroup hierarchy is travelled. This should be easy, as cpuset can be made to maintain its hierarchy. - cpuset disallows clearing cpuset.mems/cpuset.cpus if the cgroup is not empty, which can be guaranteed only by cgroup lock. - cpuset disallows a task be attached to a cgroup with empty cpuset.mems/cpuset.cpus, which again can be guarantted only by cgroup lock. - cpuset may move tasks from a cgroup to another cgroup (Glauber mentioned this). - maybe other cases I overlooked.. -- 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