Re: [Qemu-devel] vm state save/restore question

[Juan Quintela <quintela@redhat.com>]

Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
> On Wed, 2012-06-20 at 00:55 +0200, Juan Quintela wrote:
>> 
>> This was going to be my question.
>> 
>> If we can do something like: send hash register, and get a bitmap of
>> the
>> ones that get changed, we should be good.  Perhaps we need something
>> "interesting" like removing old entries (no clue if they got just
>> overwritten, or how they are replaced), and we should be good. 
>
> Right, we can do an initial "snapshot" and have the kernel start
> tracking changes from there. On the final step, we can then request from
> the kernel a new snapshot with a dirty bitmap.
>
> Or we can be even simpler, just do two snapshots and have qemu diff them
> itself :-)
>
> I am confident I can come up with something as far as the kernel and
> qemu <-> kernel interface goes. I need to get my head around the details
> on how to implement that two stage save process in qemu though and the
> corresponding restore which will need to read both snapshots and apply
> the diff before shooting it back to the kernel.
>
> BTW. Does migration in pure qemu (full system emu) works similarily, ie,
> two stage ? If it does I can easily prototype everything there.

It does, but I have no clue how the hashed page tables are implemented
on ppc, i.e. if there is anything specific for bare metal.  Alex?

Later, Juan.