Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 10 May 2018 15:07:59 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Roman Gushchin <guro@fb.com>
Cc:     kernel-team@fb.com, Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH v2] mm: fix oom_kill event handling
Message-ID: <20180510130759.GG5325@dhcp22.suse.cz>
References: <20180508124637.29984-1-guro@fb.com>
 <20180510114147.GB5325@dhcp22.suse.cz>
 <20180510121251.GA6762@castle.DHCP.thefacebook.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180510121251.GA6762@castle.DHCP.thefacebook.com>
User-Agent: Mutt/1.9.5 (2018-04-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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