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

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Message-ID: <alpine.DEB.2.10.1509291537360.3375@chino.kir.corp.google.com>
Date:	Tue, 29 Sep 2015 15:39:45 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Oleg Nesterov <oleg@...hat.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 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).

I agree your cleanup looks much better than the nested conditional.
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