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 13:12:56 +0100
From:   Roman Gushchin <guro@fb.com>
To:     Michal Hocko <mhocko@kernel.org>
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: <20180510121251.GA6762@castle.DHCP.thefacebook.com>
References: <20180508124637.29984-1-guro@fb.com>
 <20180510114147.GB5325@dhcp22.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <20180510114147.GB5325@dhcp22.suse.cz>
User-Agent: Mutt/1.9.2 (2017-12-15)
Received-SPF: None (protection.outlook.com: fb.com does not designate
 permitted sender hosts)
SpamDiagnosticOutput: 1:99
SpamDiagnosticMetadata: NSPM
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 May 2018 12:13:08.3950 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 2077c989-73bc-447d-8ea4-08d5b66f657b
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CO1PR15MB1079
X-OriginatorOrg: fb.com
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-05-10_05:,,
 signatures=0
X-Proofpoint-Spam-Reason: safe
X-FB-Internal: Safe
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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.