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SubjectRe: [patch 6/6] mm: memcg: do not trap chargers with full callstack on OOM
On Tue 30-07-13 10:32:28, Johannes Weiner wrote:
> On Tue, Jul 30, 2013 at 04:09:13PM +0200, Michal Hocko wrote:
> > On Fri 26-07-13 17:28:09, Johannes Weiner wrote:
[...]
> > > } else {
> > > schedule();
> > > + mem_cgroup_unmark_under_oom(memcg);
> > > finish_wait(&memcg_oom_waitq, &owait.wait);
> > > }
> > > - spin_lock(&memcg_oom_lock);
> > > - if (locked)
> > > - mem_cgroup_oom_unlock(memcg);
> > > - memcg_wakeup_oom(memcg);
> > > - spin_unlock(&memcg_oom_lock);
> > >
> > > - mem_cgroup_unmark_under_oom(memcg);
> > > + if (locked) {
> > > + mem_cgroup_oom_unlock(memcg);
> > > + /*
> > > + * There is no guarantee that a OOM-lock contender
> > > + * sees the wakeups triggered by the OOM kill
> > > + * uncharges. Wake any sleepers explicitely.
> > > + */
> > > + memcg_oom_recover(memcg);
> >
> > This will be a noop because memcg is no longer under_oom (you wanted
> > memcg_wakeup_oom here I guess). Moreover, even the killed wouldn't wake
> > up anybody for the same reason.
>
> Anybody entering this path will increase the under_oom counter. The
> killer decreases it again, but everybody who is sleeping because they
> failed the trylock still hasn't unmarked the hierarchy (they call
> schedule() before unmark_under_oom()). So we issue wakeups when there
> is somebody waiting for the lock.

True, sorry for the noise. Feel free to add

Acked-by: Michal Hocko <mhocko@suse.cz>
--
Michal Hocko
SUSE Labs


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