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Date: Mon, 18 Jul 2011 09:56:31 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
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To: Mel Gorman <mgorman@suse.de>
cc: Andrew Morton <akpm@linux-foundation.org>,
        Minchan Kim <minchan.kim@gmail.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mm: page allocator: Initialise ZLC for first zone
 eligible for zone_reclaim
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On Fri, 15 Jul 2011, Mel Gorman wrote:

> Currently the zonelist cache is setup only after the first zone has
> been considered and zone_reclaim() has been called. The objective was
> to avoid a costly setup but zone_reclaim is itself quite expensive. If
> it is failing regularly such as the first eligible zone having mostly
> mapped pages, the cost in scanning and allocation stalls is far higher
> than the ZLC initialisation step.

Would it not be easier to set zlc_active and allowednodes based on the
zone having an active ZLC at the start of get_pages()?

Buffered_rmqueue is handling the situation of a zone with an ZLC in a
weird way right now since it ignores the (potentially existing) ZLC
for the first pass. zlc_setup() does a lot of things. So that is because
there is a performance benefit?