linux-kernel - Re: [PATCH 3/6] mm, oom_adj: make sure processes sharing mm have same view of oom_score

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Date:	Fri, 27 May 2016 19:18:21 +0300
From:	Vladimir Davydov <vdavydov@...tuozzo.com>
To:	Michal Hocko <mhocko@...nel.org>
CC:	<linux-mm@...ck.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/6] mm, oom_adj: make sure processes sharing mm have
 same view of oom_score_adj

On Fri, May 27, 2016 at 01:18:03PM +0200, Michal Hocko wrote:
...
> @@ -1087,7 +1105,25 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
>  	unlock_task_sighand(task, &flags);
>  err_put_task:
>  	put_task_struct(task);
> +
> +	if (mm) {
> +		struct task_struct *p;
> +
> +		rcu_read_lock();
> +		for_each_process(p) {
> +			task_lock(p);
> +			if (!p->vfork_done && process_shares_mm(p, mm)) {
> +				p->signal->oom_score_adj = oom_adj;
> +				if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE))
> +					p->signal->oom_score_adj_min = (short)oom_adj;
> +			}
> +			task_unlock(p);

I.e. you write to /proc/pid1/oom_score_adj and get
/proc/pid2/oom_score_adj updated if pid1 and pid2 share mm?
IMO that looks unexpected from userspace pov.

May be, we'd better add mm->oom_score_adj and set it to the min
signal->oom_score_adj over all processes sharing it? This would
require iterating over all processes every time oom_score_adj gets
updated, but that's a slow path.