linux-kernel - Re: [PATCH -mm] proc: don't take ->siglock for /proc/pid/oom

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Date:	Thu, 1 Apr 2010 01:00:32 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	anfei <anfei.zhou@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	nishimura@....nes.nec.co.jp,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] proc: don't take ->siglock for /proc/pid/oom_adj

On 03/31, David Rientjes wrote:
>
> On Wed, 31 Mar 2010, Oleg Nesterov wrote:
>
> > David, I just can't understand why
> > 	oom-badness-heuristic-rewrite.patch
> > duplicates the related code in fs/proc/base.c and why it preserves
> > the deprecated signal->oom_adj.
>
> You could combine the two write functions together and then two read
> functions together if you'd like.

Yes,

> > 	static ssize_t oom_any_adj_write(struct file *file, const char __user *buf,
> > 						size_t count, bool deprecated_mode)
> > 	{
> >
> > 		if (depraceted_mode) {
> > 			 if (oom_score_adj == OOM_ADJUST_MAX)
> > 				oom_score_adj = OOM_SCORE_ADJ_MAX;
>
> ???

What?

> > 			 else
> > 				oom_score_adj = (oom_score_adj * OOM_SCORE_ADJ_MAX) /
> > 						-OOM_DISABLE;
> > 		}
> >
> > 		if (oom_score_adj < OOM_SCORE_ADJ_MIN ||
> > 				oom_score_adj > OOM_SCORE_ADJ_MAX)
>
> That doesn't work for depraceted_mode (sic), you'd need to test for
> OOM_ADJUST_MIN and OOM_ADJUST_MAX in that case.

Yes, probably "if (depraceted_mode)" should do more checks, I didn't try
to verify that MIN/MAX are correctly converted. I showed this code to explain
what I mean.

> There have been efforts to reuse as much of this code as possible for
> other sysctl handlers as well, you might be better off looking for

David, sorry ;) Right now I'd better try to stop the overloading of
->siglock. And, I'd like to shrink struct_signal if possible, but this
is minor.

Oleg.

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