Date: Mon, 23 Aug 2010 07:56:40 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
To: Mel Gorman <mel@csn.ul.ie>
cc: Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel List <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
        Minchan Kim <minchan.kim@gmail.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.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
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References: <1282550442-15193-1-git-send-email-mel@csn.ul.ie> <1282550442-15193-3-git-send-email-mel@csn.ul.ie>
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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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