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Date: Wed, 30 Sep 2015 15:49:43 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Kyle Walker <kwalker@redhat.com>, Michal Hocko <mhocko@kernel.org>,
        Stanislav Kozina <skozina@redhat.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH -mm 2/3] mm/oom_kill: cleanup the "kill sharing same
	memory"
Message-ID: <20150930134943.GC32263@redhat.com>
References: <20150929141818.GA10955@redhat.com> <alpine.DEB.2.10.1509291537360.3375@chino.kir.corp.google.com>
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On 09/29, David Rientjes wrote:
>
> On Tue, 29 Sep 2015, Oleg Nesterov wrote:
>
> > Purely cosmetic, but the complex "if" condition looks annoying to me.
> > Especially because it is not consistent with OOM_SCORE_ADJ_MIN check
> > which adds another if/continue.
> >
> > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> > ---
> >  mm/oom_kill.c | 22 +++++++++++++---------
> >  1 file changed, 13 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 0d581c6..8e7bed2 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -583,16 +583,20 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
> >  	 * pending fatal signal.
> >  	 */
> >  	rcu_read_lock();
> > -	for_each_process(p)
> > -		if (p->mm == mm && !same_thread_group(p, victim) &&
> > -		    !(p->flags & PF_KTHREAD)) {
> > -			if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
> > -				continue;
> > +	for_each_process(p) {
> > +		if (unlikely(p->flags & PF_KTHREAD))
> > +			continue;
> > +		if (same_thread_group(p, victim))
> > +			continue;
> > +		if (p->mm != mm)
> > +			continue;
>
> This ordering is a little weird to me, I think we would eliminate the
> majority of processes by checking for p->mm != mm first.  There are
> certainly pathological cases where that can be defeated, but in practice
> it seems to happen more often than not.
>
> Unless you object, I think the ordering should be p->mm != mm,
> same_thread_group(), unlikely(PF_KTHREAD) as it originally was (thanks for
> adding the unlikely).

OK, agreed, will send v2.

Oleg.