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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Mon, 10 Jun 2013 19:33:35 +1000
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Subject: Re: [Qemu-devel] [Qemu-ppc]  broken incoming migration
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To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Peter Lieven <pl@kamp.de>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>, Paolo Bonzini <pbonzini@redhat.com>, Wenchao Xia <xiawenc@linux.vnet.ibm.com>, David Gibson <david@gibson.dropbear.id.au>

On Mon, 2013-06-10 at 19:10 +1000, Alexey Kardashevskiy wrote:
> > I would prefer not to completely drop the patch since it saves bandwidth and
> > resources.
> 
> I would like migration to do what it should do - send pages no matter what,
> this is exactly what migration is for. If there any many, many empty pages
> (which I doubt to be a very often real life case), they could all merged in
> big consecutive chunks and sent at the end of migration.

I tend to agree. The problem of sending empty pages is purely a problem of
compression. If the current mechanism is deemed "not efficient enough" for
in the case of having lots of zero-pages, then by all means invent a better
packet format for more tightly representing them on the wire, but don't
break things by not sending them at all.

Cheers,
Ben.