Re: [PATCH v2] mm: fix oom_kill event handling

Michal Hocko
2018-05-10T13:07:59Z

On Thu 10-05-18 13:12:56, Roman Gushchin wrote:
> On Thu, May 10, 2018 at 01:41:47PM +0200, Michal Hocko wrote:
> > On Tue 08-05-18 13:46:37, Roman Gushchin wrote:
> > > Commit e27be240df53 ("mm: memcg: make sure memory.events is
> > > uptodate when waking pollers") converted most of memcg event
> > > counters to per-memcg atomics, which made them less confusing
> > > for a user. The "oom_kill" counter remained untouched, so now
> > > it behaves differently than other counters (including "oom").
> > > This adds nothing but confusion.
> > >
> > > Let's fix this by adding the MEMCG_OOM_KILL event, and follow
> > > the MEMCG_OOM approach. This also removes a hack from
> > > count_memcg_event_mm(), introduced earlier specially for the
> > > OOM_KILL counter.
> >
> > I agree that the current OOM_KILL is confusing. But do we really need
> > another memcg_memory_event_mm helper used for only one counter rather
> > than reuse memcg_memory_event. __oom_kill_process doesn't have the memcg
> > but nothing should really prevent us from adding the context
> > (oom_control) there, no?
>
> Not sure, that I follow. oom_control has memcg pointer,
> but it's a pointer to a cgroup, where OOM happened.
> In particular, it's NULL for a system-wide OOM.
>
> And we do send the OOM_KILL event to the cgroup,
> which actually contains the process.

You are right! For some reason I thought we do count events on the
hierarchy which is under OOM. I was wrong.

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