Migration with linear p2m list

Migration with linear p2m list

[Juergen Gross]

I'm just working on a patch series to support migration via using
the virtual mapped linear p2m list. Migration seems to work quite
nice and now I'm looking into how to support changes of the p2m
list structure during migration. For this purpose we introduced
p2m_generation in the shared info structure which is incremented
by the guest in case of changing a mapping of the p2m list.

The question is: what kind of support should I add initially:

1) none: same as for the p2m tree used today

2) minimal: detect a change and cancel migration in this case

3) medium: detect a change and restart migration (limited by a
   retry count)

4) full: detect a change and adapt the current migration to it
   (remap p2m list, resend it to receive side, adapt logdirty
   map)

As such a change should be rare I'm currently heading for the
minimal solution. Full support could be added later independent
from the initial p2m list support. Any thoughts?


Juergen

Re: Migration with linear p2m list

[Andrew Cooper]

On 03/12/15 07:41, Juergen Gross wrote:
> I'm just working on a patch series to support migration via using
> the virtual mapped linear p2m list. Migration seems to work quite
> nice and now I'm looking into how to support changes of the p2m
> list structure during migration. For this purpose we introduced
> p2m_generation in the shared info structure which is incremented
> by the guest in case of changing a mapping of the p2m list.
>
> The question is: what kind of support should I add initially:
>
> 1) none: same as for the p2m tree used today
>
> 2) minimal: detect a change and cancel migration in this case
>
> 3) medium: detect a change and restart migration (limited by a
>    retry count)
>
> 4) full: detect a change and adapt the current migration to it
>    (remap p2m list, resend it to receive side, adapt logdirty
>    map)
>
> As such a change should be rare I'm currently heading for the
> minimal solution. Full support could be added later independent
> from the initial p2m list support. Any thoughts?

I would also opt for 2 to start with.

There is a substantial quantity of other infrastructure required to
correctly send an update once you have noticed that something has
changed.  It would be better not to conflate the two issues.

~Andrew