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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Date:	Mon, 23 Aug 2010 07:56:40 -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:

> This patch introduces zone_nr_free_pages() to take a slightly more accurate
> estimate of NR_FREE_PAGES while kswapd is awake. The estimate is not perfect
> and may result in cache line bounces but is expected to be lighter than the
> IPI calls necessary to continually drain the per-cpu counters while kswapd
> is awake.

The delta of the counters could also be reduced to increase accuracy.
See refresh_zone_stat_thresholds().

Also would it be possible to add the summation function to vmstat? It may
be useful elsewhere.

A new function like

	zone_page_state_snapshot()

or so?


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