Message-ID: <49D11674.9040205@goop.org>
Date: Mon, 30 Mar 2009 11:59:00 -0700
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: Rik van Riel <riel@redhat.com>
CC: Dave Hansen <dave@linux.vnet.ibm.com>,
       Martin Schwidefsky <schwidefsky@de.ibm.com>, akpm@osdl.org,
       nickpiggin@yahoo.com.au, frankeh@watson.ibm.com,
       virtualization@lists.osdl.org, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, hugh@veritas.com
Subject: Re: [patch 0/6] Guest page hinting version 7.
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Rik van Riel wrote:
> Jeremy Fitzhardinge wrote:
>
>> That said, people have been looking at tracking block IO to work out 
>> when it might be useful to try and share pages between guests under Xen.
>
> Tracking block IO seems like a bass-ackwards way to figure
> out what the contents of a memory page are.

Well, they're research projects, so nobody said that they're necessarily 
useful results ;).  I think the rationale is that, in general, there 
aren't all that many sharable pages, and asize from zero-pages, the bulk 
of them are the result of IO.  Since its much simpler to compare 
device+block references than doing page content matching, it is worth 
looking at the IO stream to work out what your candidates are.

> The KVM KSM code has a simpler, yet still efficient, way of
> figuring out which memory pages can be shared.
How's that?  Does it do page content comparison?

    J

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