* KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-03-31 15:13:56]:
> On Tue, 30 Mar 2010 23:07:08 -0700 (PDT)
> David Rientjes <rientjes@xxxxxxxxxx> wrote:
>
> > On Wed, 31 Mar 2010, KAMEZAWA Hiroyuki wrote:
> >
> > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > > > > index 0cb1ca4..9e89a29 100644
> > > > > --- a/mm/oom_kill.c
> > > > > +++ b/mm/oom_kill.c
> > > > > @@ -510,8 +510,10 @@ retry:
> > > > > if (PTR_ERR(p) == -1UL)
> > > > > goto out;
> > > > >
> > > > > - if (!p)
> > > > > - p = current;
> > > > > + if (!p) {
> > > > > + read_unlock(&tasklist_lock);
> > > > > + panic("Out of memory and no killable processes...\n");
> > > > > + }
> > > > >
> > > > > if (oom_kill_process(p, gfp_mask, 0, points, limit, mem,
> > > > > "Memory cgroup out of memory"))
> > > > >
> > > >
> > > > This actually does appear to be necessary but for a different reason: if
> > > > current is unkillable because it has OOM_DISABLE, for example, then
> > > > oom_kill_process() will repeatedly fail and mem_cgroup_out_of_memory()
> > > > will infinitely loop.
> > > >
> > > > Kame-san?
> > > >
> > >
> > > When a memcg goes into OOM and it only has unkillable processes (OOM_DISABLE),
> > > we can do nothing. (we can't panic because container's death != system death.)
> > >
> > > Because memcg itself has mutex+waitqueue for mutual execusion of OOM killer,
> > > I think infinite-loop will not be critical probelm for the whole system.
> > >
> > > And, now, memcg has oom-kill-disable + oom-kill-notifier features.
> > > So, If a memcg goes into OOM and there is no killable process, but oom-kill is
> > > not disabled by memcg.....it means system admin's mis-configuraton.
> > >
> > > He can stop inifite loop by hand, anyway.
> > > # echo 1 > ..../group_A/memory.oom_control
> > >
> >
> > Then we should be able to do this since current is by definition
> > unkillable since it was not found in select_bad_process(), right?
>
> To me, this patch is acceptable and seems reasnoable.
>
> But I didn't joined to memcg development when this check was added
> and don't know why kill current..
>
The reason for adding current was that we did not want to loop
forever, since it stops forward progress - no error/no forward
progress. It made sense to oom kill the current process, so that the
cgroup admin could look at what went wrong.
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=c7ba5c9e8176704bfac0729875fa62798037584d
>
> Addinc Balbir to CC. Maybe situation is changed now.
> Because we can stop inifinite loop (by hand) and there is no rushing oom-kill
> callers, this change is acceptable.
>
By hand is not always possible if we have a large number of cgroups
(I've seen a setup with 2000 cgroups on libcgroup ML). 2000 cgroups *
number of processes make the situation complex. I think using OOM
notifier is now another way of handling such a situation.
--
Three Cheers,
Balbir
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