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SubjectRe: [PATCH 0/2] memcg: cgroup fix rmdir hang
On Tue, 23 Jun 2009 16:07:20 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> previous discussion was this => http://marc.info/?t=124478543600001&r=1&w=2
>
> This patch tries to fix problem as
> - rmdir can sleep very very long if swap entry is shared between multiple
> cgroups
>
> Now, cgroup's rmdir path does following
>
> ==
> again:
> check there are no tasks and children group.
> call pre_destroy()
> check css's refcnt
> if (refcnt > 0) {
> sleep until css's refcnt goes down to 0.
> goto again
> }
> ==
>
> Unfortunately, memory cgroup does following at charge.
>
> css_get(&memcg->css)
> ....
> charge(memcg) (increase USAGE)
> ...
> And this "memcg" is not necessary to include the caller, task.
>
> pre_destroy() tries to reduce memory usage until USAGE goes down to 0.
> Then, there is a race that
> - css's refcnt > 0 (and memcg's usage > 0)
> - rmdir() caller sleeps until css->refcnt goes down 0.
> - But to make css->refcnt be 0, pre_destroy() should be called again.
>
> This patch tries to fix this in asyhcnrounos way (i.e. without big lock.)
> Any comments are welcome.
>

Do you believe that these fixes should be backported into 2.6.30.x?


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