linux-kernel - Re: [PATCH 4/5] oom: the points calculation of child processes must use find_lock_task

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Message-ID: <20100531165658.GC9991@redhat.com>
Date:	Mon, 31 May 2010 18:56:58 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 4/5] oom: the points calculation of child processes
	must use find_lock_task_mm() too

On 05/31, KOSAKI Motohiro wrote:
>
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -87,6 +87,7 @@ static struct task_struct *find_lock_task_mm(struct task_struct *p)
>  unsigned long badness(struct task_struct *p, unsigned long uptime)
>  {
>  	unsigned long points, cpu_time, run_time;
> +	struct task_struct *c;
>  	struct task_struct *child;
>  	int oom_adj = p->signal->oom_adj;
>  	struct task_cputime task_time;
> @@ -124,11 +125,13 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
>  	 * child is eating the vast majority of memory, adding only half
>  	 * to the parents will make the child our kill candidate of choice.
>  	 */
> -	list_for_each_entry(child, &p->children, sibling) {
> -		task_lock(child);
> -		if (child->mm != p->mm && child->mm)
> -			points += child->mm->total_vm/2 + 1;
> -		task_unlock(child);
> +	list_for_each_entry(c, &p->children, sibling) {
> +		child = find_lock_task_mm(c);
> +		if (child) {
> +			if (child->mm != p->mm)
> +				points += child->mm->total_vm/2 + 1;
> +			task_unlock(child);
> +		}

Acked-by: Oleg Nesterov <oleg@...hat.com>




And, I think we need another patch on top of this one. Note that
this list_for_each_entry(p->children) can only see the tasks forked
by p, it can't see other children forked by its sub-threads.

IOW, we need

	do {
		list_for_each_entry(c, &t->children, sibling) {
			...
		}
	} while_each_thread(p, t);

Probably the same for oom_kill_process().

What do you think?

Oleg.

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