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: <alpine.DEB.2.00.1008231059580.8601@router.home>
Date:	Mon, 23 Aug 2010 11:04:38 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Mel Gorman <mel@....ul.ie>
cc:	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>,
	KOSAKI Motohiro <kosaki.motohiro@...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 Mon, 23 Aug 2010, Mel Gorman wrote:

> > When the vm gets into a state where continual reclaim is necessary then
> > the counters are not that frequently updated. If the machine is already
> > slowing down due to reclaim then the vm can likely affort more frequent
> > counter updates.
> >
>
> Ok, but is that better than this patch? Decreasing the size of the window by
> reducing the threshold still leaves a window. There is still a small amount
> of drift by summing up all the deltas but you get a much more accurate count
> at the point of time it was important to know.

In order to make that decision we would need to know what deltas make a
significant difference. Would be also important to know if there are any
other counters that have issues. If so then the reduction of the
thresholds is addressing these problems in a number of counters.

I have no objection against this approach here but it may just be bandaid
on a larger issue that could be approached in a cleaner way.

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