Re: [Qemu-devel] [RFC]VM live snapshot proposal

[Kevin Wolf]

Am 03.03.2014 um 14:19 hat Paolo Bonzini geschrieben:
> Il 03/03/2014 13:55, Kevin Wolf ha scritto:
> >>>> > Due to memory-modifications may happen in kvm, qemu, or vhost, the 
> >>>> > key-part is how we
> >>>> > can provide common page-modify-tracking-and-saving api, we completed a 
> >>>> > prototype by
> >>>> > simply add modified-page tracking/saving function in qemu, and it 
> >>>> > seems worked fine.
> >>>
> >>> Yes, this is the tricky part.  To be honest, I think this is the reason
> >>> no one has submitted patches - it's a hard task and the win isn't that
> >>> great (you can already migrate to file).
> >So why don't we simply reuse the existing migration code?
> 
> I think this is different in the same way that block-backup and
> block-mirror are different.  Huangpeng's proposal would let you make
> a consistent snapshot of disks and RAM.

Right. Though the point isn't about consistency (doing the disk snapshot
when memory has converged would be consistent as well), but about
having the snapshot semantically right at the time when the monitor
command is issued instead of only starting it then and being consistent
at the point of completion.

This is indeed like pre/post-copy live migration, and probably both
options have their uses. I would suggest starting with the easy one, and
adding the post-copy feature on top.

Kevin