linux-kernel - Re: [PATCH v2] mm: fix oom

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Message-ID: <20180510121251.GA6762@castle.DHCP.thefacebook.com>
Date:   Thu, 10 May 2018 13:12:56 +0100
From:   Roman Gushchin <guro@...com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     <kernel-team@...com>, Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        <linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
        <linux-mm@...ck.org>
Subject: Re: [PATCH v2] mm: fix oom_kill event handling

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.