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

[Roman Gushchin]

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.