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SubjectRe: [PATCH v2] mm/oom_kill: count global and memory cgroup oom kills
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On 13.09.2017 07:51, PINTU KUMAR wrote:
>
>
> Hi,
>
> I have submitted a similar patch 2 years ago (Oct/2015).
> But at that time the patch was rejected.
> Here is the history:
> https://lkml.org/lkml/2015/10/1/372
>
> Now I see the similar patch got accepted. At least the initial idea and the objective were same.
> Even I were not included here.
> On one side I feel happy that my initial idea got accepted now.
> But on the other side it really hurts :(
>

If this makes you feel better: mine version also fixes uncertainty in memory cgroup statistics.

>
> Thanks,
> Pintu
>
>
> On Monday 5 June 2017, 7:57:57 PM IST, Konstantin Khlebnikov <khlebnikov@yandex-team.ru> wrote:
>
>
> On 05.06.2017 11:50, Michal Hocko wrote:
> > On Thu 25-05-17 13:28:30, Konstantin Khlebnikov wrote:
> >> Show count of oom killer invocations in /proc/vmstat and count of
> >> processes killed in memory cgroup in knob "memory.events"
> >> (in memory.oom_control for v1 cgroup).
> >>
> >> Also describe difference between "oom" and "oom_kill" in memory
> >> cgroup documentation. Currently oom in memory cgroup kills tasks
> >> iff shortage has happened inside page fault.
> >>
> >> These counters helps in monitoring oom kills - for now
> >> the only way is grepping for magic words in kernel log.
> >
> > Yes this is less than optimal and the counter sounds like a good step
> > forward. I have 2 comments to the patch though.
> >
> > [...]
> >
> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> >> index 899949bbb2f9..42296f7001da 100644
> >> --- a/include/linux/memcontrol.h
> >> +++ b/include/linux/memcontrol.h
> >> @@ -556,8 +556,11 @@ static inline void mem_cgroup_count_vm_event(struct mm_struct *mm,
> >>
> >> rcu_read_lock();
> >> memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
> >> - if (likely(memcg))
> >> + if (likely(memcg)) {
> >> this_cpu_inc(memcg->stat->events[idx]);
> >> + if (idx == OOM_KILL)
> >> + cgroup_file_notify(&memcg->events_file);
> >> + }
> >> rcu_read_unlock();
> >
> > Well, this is ugly. I see how you want to share the global counter and
> > the memcg event which needs the notification. But I cannot say this
> > would be really easy to follow. Can we have at least a comment in
> > memcg_event_item enum definition?
>
> Yep, this is a little bit ugly.
> But this funciton is static-inline and idx always constant so resulting code is fine.
>
> >
> >> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> >> index 04c9143a8625..dd30a045ef5b 100644
> >> --- a/mm/oom_kill.c
> >> +++ b/mm/oom_kill.c
> >> @@ -876,6 +876,11 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
> >> /* Get a reference to safely compare mm after task_unlock(victim) */
> >> mm = victim->mm;
> >> mmgrab(mm);
> >> +
> >> + /* Raise event before sending signal: reaper must see this */
> >> + count_vm_event(OOM_KILL);
> >> + mem_cgroup_count_vm_event(mm, OOM_KILL);
> >> +
> >> /*
> >> * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
> >> * the OOM victim from depleting the memory reserves from the user
> >
> > Why don't you count tasks which share mm with the oom victim?
>
> Yes, this makes sense. But these kills are not logged thus counter will differs from logged events.
> Also these tasks might live in different cgroups, so counting to mm owner isn't correct.
>
>
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 0e2c925e7826..9a95947a60ba 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -924,6 +924,8 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
> > */
> > if (unlikely(p->flags & PF_KTHREAD))
> > continue;
> > + count_vm_event(OOM_KILL);
> > + count_memcg_event_mm(mm, OOM_KILL);
> > do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
> > }
> > rcu_read_unlock();
> >
> > Other than that looks good to me.
> > Acked-by: Michal Hocko <mhocko@suse.com>
> >
>
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