Messages in this thread | | | Date | Fri, 26 Jun 2009 08:29:56 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 0/2] memcg: cgroup fix rmdir hang |
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On Thu, 25 Jun 2009 14:28:09 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> 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?
Yes, I think so. (If it's easy)
To be honest:
To cause the problem, - swap cgroup should be shared between cgroup. - rmdir should be called in critical chance.
Considering usual usage of cgroup is "container", there will be no share of swap in typical users. But, 2.6.30 can be a base kernel of a major distro. So, I hope this in 2.6.30 if we have no difficulties.
Thanks, -Kame
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