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SubjectRe: [Experimental][PATCH 19/21] memcg-fix-pre-destroy.patch
On Thu, 4 Dec 2008 18:43:09 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> 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.
> ==
Ah, anyway, I'll remove mem->refcnt when swap-cgroup uses this ID.
I'll use refcnt-to-ID rather than this.

Thanks,
-Kame






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