linux-kernel - Re: [PATCH -mm 2/3] mm/oom_kill: cleanup the "kill sharing same memory"

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Date:	Wed, 30 Sep 2015 15:49:43 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Kyle Walker <kwalker@...hat.com>,
	Michal Hocko <mhocko@...nel.org>,
	Stanislav Kozina <skozina@...hat.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 2/3] mm/oom_kill: cleanup the "kill sharing same
	memory"

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@...hat.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.

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