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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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