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Date: Fri, 20 May 2016 03:50:01 +0200
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH v3] mm,oom: speed up select_bad_process() loop.
Message-ID: <20160520015000.GA20132@redhat.com>
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To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, rientjes@google.com, linux-mm@kvack.org

On 05/19, Michal Hocko wrote:
>
> Long term I
> would like to to move this logic into the mm_struct, it would be just
> larger surgery I guess.

Why we can't do this right now? Just another MMF_ flag set only once and
never cleared.

And. I personally like this change "in general", if nothing else I recently
blamed this for_each_process_thread() loop. But if we do this, I think we
should also shift find_lock_task_mm() into this loop.

And this makes me think again we need something like

	struct task_struct *next_task_with_mm(struct task_struct *p)
	{
		struct task_struct *t;

		p = p->group_leader;
		while ((p = next_task(p)) != &init_task) {
			if (p->flags & PF_KTHREAD)
				continue;

			t = find_lock_task_mm(p);
			if (t)
				return t;
		}

		return NULL;
	}

	#define for_each_task_lock_mm(p)
		for (p = &init_task; (p = next_task_with_mm(p)); task_unlock(p))

Or we we can move task_unlock() into next_task_with_mm(), it can check mm != NULL
or p != init_task.

Oleg.

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