Date: Mon, 23 Aug 2010 11:04:38 -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
In-Reply-To: <20100823135559.GS19797@csn.ul.ie>
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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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