Re: [Xen-devel] [PATCH 1/2] PV hugepages - Xen patch

[Dave McCracken <dcm@xxxxxxxx>]

On Wednesday 08 October 2008, Keir Fraser wrote:
> On 8/10/08 18:05, "Dave McCracken" <dcm@xxxxxxxx> wrote:
> > On Friday 03 October 2008, Keir Fraser wrote:
> >>  * This surely breaks save/restore, since the restore code is not
> >> superpage-aware.
> >
> > I don't have this one solved yet.  I'm working on it.
>
> Actually this is an interesting one. For a PV guest it may be in general
> unsolvable, since the target machine may not have allocatable 2MB extents.
> It may also screw live migration since 2MB is a very coarse granularity to
> do dirty-page tracking. One option: perhaps the PV kernel could shatter and
> then reconstruct (as best it can) superpage mappings across save/restore?
> I'm actually not sure what's for the best here. Perhaps just make 2MB
> mappings and save/restore mutually exclusive for now?

Yeah, that's what I'm finding.  I think it's a good idea to document for now 
that hugepages don't work with save/restore.  I'll continue to dig into it 
and try to figure out a scheme to make it work as a future enhancement.

Dave McCracken

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