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Re: [Qemu-devel] [Qemu-ppc] broken incoming migration

From: Peter Lieven
Subject: Re: [Qemu-devel] [Qemu-ppc] broken incoming migration
Date: Mon, 10 Jun 2013 11:42:25 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6

On 10.06.2013 11:33, Benjamin Herrenschmidt wrote:
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
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.

Ok, I see the point. I think the paradigm to say that the destination
should "decide" if it needs a page or not is a sound one.

Zero pages are quite often depending on the lifetime and the operating
system used. But a consecutive range of zero pages is only likely
in the bulk stage. I don't know if its reasonable to add a special encoding
for that.

I will sent a v2 of my previous revert patch addressing Erics concerns shortly.


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