linux-kernel - Re: [patch 1/2] oom: remove oom_disable

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Message-ID: <20110830152856.GA22754@redhat.com>
Date:	Tue, 30 Aug 2011 17:28:56 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ying Han <yinghan@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch 1/2] oom: remove oom_disable_count

On 08/30, David Rientjes wrote:
>
> This removes mm->oom_disable_count entirely since it's unnecessary and
> currently buggy.  The counter was intended to be per-process but it's
> currently decremented in the exit path for each thread that exits, causing
> it to underflow.
>
> The count was originally intended to prevent oom killing threads that
> share memory with threads that cannot be killed since it doesn't lead to
> future memory freeing.  The counter could be fixed to represent all
> threads sharing the same mm, but it's better to remove the count since:
>
>  - it is possible that the OOM_DISABLE thread sharing memory with the
>    victim is waiting on that thread to exit and will actually cause
>    future memory freeing, and
>
>  - there is no guarantee that a thread is disabled from oom killing just
>    because another thread sharing its mm is oom disabled.

Great, thanks.

Even _if_ (I hope not) we decide to re-introduce this counter later,
I think it will be much more simple to start from the very beginning
and make the correct patch.

> @@ -447,6 +431,9 @@ static int oom_kill_task(struct task_struct *p, struct mem_cgroup *mem)
>  	for_each_process(q)
>  		if (q->mm == mm && !same_thread_group(q, p) &&
>  		    !(q->flags & PF_KTHREAD)) {

(I guess this is on top of -mm patch)

> +			if (q->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
> +				continue;
> +

Afaics, this is the only change apart from "removes mm->oom_disable_count
entirely", looks reasonable to me.

Oleg.

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