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Date: Mon, 31 Oct 2011 11:14:49 +0800 From: Li Zefan <lizf@...fujitsu.com> To: Frederic Weisbecker <fweisbec@...il.com> CC: Ben Blum <bblum@...rew.cmu.edu>, Andrew Morton <akpm@...ux-foundation.org>, Frederic Weisbecker <fweisbec@...hat.com>, Paul Menage <paul@...lmenage.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] cgroups: don't cache common ancestor in task counter subsys Frederic Weisbecker wrote: > On Mon, Oct 17, 2011 at 01:27:53PM -0400, Ben Blum wrote: >> On Mon, Oct 17, 2011 at 07:25:41PM +0200, Frederic Weisbecker wrote: >>> When we rollback there, we are dealing with oldcgrp of the last thread >>> we have treated. All threads in the rollback list don't necessary belonged >>> to that old_cgroup. >>> >>> And we can't try to retrieve these old_cgroup through task_cgroup_from_root() because >>> the threads might have exited and thus could be assigned to the init cgroup. >>> >>> I believe we need to cache these old cgroups in the flex array. >>> >> >> Doing this would fulfill the "TODO" in cgroup_attach_proc for being able >> to pass the oldcgrp for each task in the loop around the ss->attach >> call, so if you do that, remove the corresponding comment. :) >> >> -- Ben > > I don't know, looking at the code, there is a separate issue to solve there. > The old cgroup passed in ->attach() is the one of a random task from the thread > group. The migrations that happen right before leave oldcgrp with the > old cgroup of the last thread in the group. > > This doesn't seem to make any sense. As far as I checked this is only used > by the cpuset subsystem that does a migration in cpuset_attach() from > the old cgroup to the new. > > I'm not sure about the details but that looks buggy. > I think you're right, and Tejun's patchset happens to fix this bug in cpuset_attach() - it gets the mm of the thread leader and do migration. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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