Re: Migration with linear p2m list

[Andrew Cooper <andrew.cooper3@citrix.com>]

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