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Date: Wed, 12 Dec 2012 11:00:22 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH 0/2] live backup vm
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To: Dietmar Maurer <dietmar@proxmox.com>
Cc: "kwolf@redhat.com" <kwolf@redhat.com>, "stefanha@gmail.com" <stefanha@gmail.com>, "aliguori@us.ibm.com" <aliguori@us.ibm.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "blauwirbel@gmail.com" <blauwirbel@gmail.com>

Il 12/12/2012 10:03, Dietmar Maurer ha scritto:
>>> So our snapshot implementation uses the following steps:
>>>
>>> 1.) qmp: savevm-start [statefile]
>>>
>>> This save the VM state into [statefile] and then stops the VM.
>>
>> That's migrate exec:cat>statefile (or similar)
> 
> We save to block devices, so we need to allocate them in advance
> with a size of 2 x 'memory size'.
> So we have an upper limit for the state file file, i.e. we stop the
> VM if ('statefile size' > 'assigned memory').

This is a heuristic that we can add (though remember you'll need some
extra space for the device state).

> It would be great to have some other means to reduce state size (instead 
> of stopping the VM), for example by slowing down the VM somehow? 

Yes, you can use the cpu cgroup.

Paolo

> Any other ideas?
>