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Date: Wed, 12 Jun 2013 16:10:38 -0400
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [Qemu-ppc]  broken incoming migration
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>, Peter Lieven <pl@kamp.de>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>, Wenchao Xia <xiawenc@linux.vnet.ibm.com>, David Gibson <david@gibson.dropbear.id.au>

Il 12/06/2013 10:11, Benjamin Herrenschmidt ha scritto:
> On Wed, 2013-06-12 at 10:00 -0400, Paolo Bonzini wrote:
>> The only bug we have is not a performance bug related to compression;
>> it's that writing zero pages breaks overcommit.  Let's fix that, and
>> only that.
> 
> Right, do we have a way to madvise "throw away" these instead ?

We already do that, but apparently that madvise is asynchronous.

> Or do we
> have a way to track that the platform init code did write something
> there and only clear *those* pages ?

No need for; since it's copy-on-write, not copy-on-read :) we can just
check for pages that are zero and not rewrite them with zeros.  That's
what Peter's patches do, I'll review them right away.

Paolo