linux-kernel - Re: [PATCH 2/3] mm: page allocator: Calculate a better estimate of NR_FREE_PAGES when memory is low and kswapd is awake

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Message-Id: <20100902092628.D065.A69D9226@jp.fujitsu.com>
Date:	Thu,  2 Sep 2010 09:26:57 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	kosaki.motohiro@...fujitsu.com, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 2/3] mm: page allocator: Calculate a better estimate of NR_FREE_PAGES when memory is low and kswapd is awake

> On Wed, 1 Sep 2010, Mel Gorman wrote:
> 
> > > > >         if (delta < 0 && abs(delta) > nr_free_pages)
> > > > >                 delta = -nr_free_pages;
> > >
> > > Not sure what the point here is. If the delta is going below zero then
> > > there was a concurrent operation updating the counters negatively while
> > > we summed up the counters.
> >
> > The point is if the negative delta is greater than the current value of
> > nr_free_pages then nr_free_pages would underflow when delta is applied to it.
> 
> Ok. then
> 
> 	nr_free_pages += delta;
> 	if (nr_free_pages < 0)
> 		nr_free_pages = 0;

nr_free_pages is unsined. this wouldn't works ;)




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