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SubjectRe: [Experimental][PATCH 19/21] memcg-fix-pre-destroy.patch
On Thu, 4 Dec 2008 18:34:28 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> Added CC: Paul Menage <menage@google.com>
>
> > @@ -2096,7 +2112,7 @@ static void mem_cgroup_get(struct mem_cg
> > static void mem_cgroup_put(struct mem_cgroup *mem)
> > {
> > if (atomic_dec_and_test(&mem->refcnt)) {
> > - if (!mem->obsolete)
> > + if (!css_under_removal(&mem->css))
> > return;
> > mem_cgroup_free(mem);
> > }
> I don't think it's safe to check css_under_removal here w/o cgroup_lock.
> (It's safe *NOW* just because memcg is the only user of css->refcnt.)
>

> As Li said before, css_under_removal doesn't necessarily mean
> this this group has been destroyed, but mem_cgroup will be freed.
>
> But adding cgroup_lock/unlock here causes another dead lock,
> because mem_cgroup_get_next_node calls mem_cgroup_put.
>
> hmm.. hierarchical reclaim code will be re-written completely by [21/21],
> so would it be better to change patch order or to take another approach ?
>
Hmm, ok.

How about this ?
==
At initlization, mem_cgroup_create(), set memcg->refcnt to be 1.

At destroy(), put this refcnt by 1.

remove css_under_removal(&mem->css) check.
==

-Kame



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