Re: [Qemu-devel] [PATCH 11/17] pseries: savevm support for pseries machine

[Anthony Liguori <aliguori@us.ibm.com>]

Alexander Graf <agraf@suse.de> writes:

> On 08.07.2013, at 20:45, Anthony Liguori wrote:
>
>> Alexey Kardashevskiy <aik@ozlabs.ru> writes:
>> 
>>> From: David Gibson <david@gibson.dropbear.id.au>
>>> 
>>> This adds the necessary pieces to implement savevm / migration for the
>>> pseries machine.  The most complex part here is migrating the hash
>>> table - for the paravirtualized pseries machine the guest's hash page
>>> table is not stored within guest memory, but externally and the guest
>>> accesses it via hypercalls.
>>> 
>>> This patch uses a hypervisor reserved bit of the HPTE as a dirty bit
>>> (tracking changes to the HPTE itself, not the page it references).
>>> This is used to implement a live migration style incremental save and
>>> restore of the hash table contents.
>>> 
>>> In addition it adds VMStateDescription information to save and restore
>>> the (few) remaining pieces of state information needed by the pseries
>>> machine.
>>> 
>>> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> 
>> I vaguely recall making the suggestion to use a live section like this.
>> How large is the HTAB typically?
>
> The default for HV KVM is at 16MB IIRC.

And if I recall since it's a hash table, updates are random access and
not at all page aligned making using qemu ram quite unusable for this
purpose.

I guess:

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>

Regards,

Anthony Liguori


>
>
> Alex