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Date: Thu, 06 Aug 2009 14:44:01 +0300
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [RFC] respect the referenced bit of KVM guest pages?
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To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Rik van Riel <riel@redhat.com>, "Dike, Jeffrey G" <jeffrey.g.dike@intel.com>, "Yu, Wilfred" <wilfred.yu@intel.com>, "Kleen, Andi" <andi.kleen@intel.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Andrew Morton <akpm@linux-foundation.org>, Christoph Lameter <cl@linux-foundation.org>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Mel Gorman <mel@csn.ul.ie>, LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>
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On 08/06/2009 01:59 PM, Wu Fengguang wrote:
>
> This is a quick hack to materialize the idea. It remembers roughly
> the last 32*SWAP_CLUSTER_MAX=1024 active (mapped) pages scanned,
> and if _all of them_ are referenced, then the referenced bit is
> probably meaningless and should not be taken seriously.
>
>    

I don't think we should ignore the referenced bit. There could still be 
a large batch of unreferenced pages later on that we should 
preferentially swap. If we swap at least 1 page for every 250 scanned, 
after 4K swaps we will have traversed 1M pages, enough to find them.

> As a refinement, the static variable 'recent_all_referenced' could be
> moved to struct zone or made a per-cpu variable.
>
>    

Definitely this should be made part of the zone structure, consider the 
original report where the problem occurs in a 128MB zone (where we can 
expect many pages to have their referenced bit set).

-- 
error compiling committee.c: too many arguments to function

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