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Date: Wed, 12 Jun 2013 10:00:37 -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 08/06/2013 22:53, Benjamin Herrenschmidt ha scritto:
> On Sun, 2013-06-09 at 10:16 +0800, Wenchao Xia wrote:
>>    If an page was not received and destination knows that page should
>> exist according to total size, fill it with zero at destination, would
>> it solve the problem?
> 
> The easiest way to do that is to not write to those pages at the
> destination to begin with, when initializing the VM... Is there any way
> to know that a VM is being setup as a migration target or not ?

There is the "incoming" variable in vl.c (currently not a global), but I
suspect Peter's patch could have also broken loadvm.  It could quickly
become a rat hole.

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.

Paolo