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    SubjectRe: [PATCH RFC] memcg: fix drain_all_stock crash
    On Tue 09-08-11 19:07:25, KAMEZAWA Hiroyuki wrote:
    > On Tue, 9 Aug 2011 12:09:44 +0200
    > Michal Hocko <mhocko@suse.cz> wrote:
    >
    > > On Tue 09-08-11 18:53:13, KAMEZAWA Hiroyuki wrote:
    > > > On Tue, 9 Aug 2011 11:45:03 +0200
    > > > Michal Hocko <mhocko@suse.cz> wrote:
    > > >
    > > > > On Tue 09-08-11 18:32:16, KAMEZAWA Hiroyuki wrote:
    > > > > > On Tue, 9 Aug 2011 11:31:50 +0200
    > > > > > Michal Hocko <mhocko@suse.cz> wrote:
    > > > > >
    > > > > > > What do you think about the half backed patch bellow? I didn't manage to
    > > > > > > test it yet but I guess it should help. I hate asymmetry of drain_lock
    > > > > > > locking (it is acquired somewhere else than it is released which is
    > > > > > > not). I will think about a nicer way how to do it.
    > > > > > > Maybe I should also split the rcu part in a separate patch.
    > > > > > >
    > > > > > > What do you think?
    > > > > >
    > > > > >
    > > > > > I'd like to revert 8521fc50 first and consider total design change
    > > > > > rather than ad-hoc fix.
    > > > >
    > > > > Agreed. Revert should go into 3.0 stable as well. Although the global
    > > > > mutex is buggy we have that behavior for a long time without any reports.
    > > > > We should address it but it can wait for 3.2.
    > >
    > > I will send the revert request to Linus.
    > >
    > > > What "buggy" means here ? "problematic" or "cause OOps ?"
    > >
    > > I have described that in an earlier email. Consider pathological case
    > > when CPU0 wants to async. drain a memcg which has a lot of cached charges while
    > > CPU1 is already draining so it holds the mutex. CPU0 backs off so it has
    > > to reclaim although we could prevent from it by getting rid of cached
    > > charges. This is not critical though.
    > >
    >
    > That problem should be fixed by background reclaim.

    How? Do you plan to rework locking or the charge caching completely?

    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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