linux-kernel - Re: [v10 3/6] mm, oom: cgroup-aware OOM killer

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Message-ID: <20171004203138.GA2632@cmpxchg.org>
Date:   Wed, 4 Oct 2017 16:31:38 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, kernel-team@...com,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v10 3/6] mm, oom: cgroup-aware OOM killer

On Wed, Oct 04, 2017 at 01:17:14PM -0700, David Rientjes wrote:
> On Wed, 4 Oct 2017, Roman Gushchin wrote:
> 
> > > > @@ -828,6 +828,12 @@ static void __oom_kill_process(struct task_struct *victim)
> > > >  	struct mm_struct *mm;
> > > >  	bool can_oom_reap = true;
> > > >  
> > > > +	if (is_global_init(victim) || (victim->flags & PF_KTHREAD) ||
> > > > +	    victim->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
> > > > +		put_task_struct(victim);
> > > > +		return;
> > > > +	}
> > > > +
> > > >  	p = find_lock_task_mm(victim);
> > > >  	if (!p) {
> > > >  		put_task_struct(victim);
> > > 
> > > Is this necessary? The callers of this function use oom_badness() to
> > > find a victim, and that filters init, kthread, OOM_SCORE_ADJ_MIN.
> > 
> > It is. __oom_kill_process() is used to kill all processes belonging
> > to the selected memory cgroup, so we should perform these checks
> > to avoid killing unkillable processes.
> > 
> 
> That's only true after the next patch in the series which uses the 
> oom_kill_memcg_member() callback to kill processes for oom_group, correct?  
> Would it be possible to move this check to that patch so it's more 
> obvious?

Yup, I realized it when reviewing the next patch. Moving this hunk to
the next patch would probably make sense. Although, us reviewers have
been made aware of this now, so I don't feel strongly about it. Won't
make much of a difference once the patches are merged.