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Re: [Xen-devel] map memory holes with same page

At 11:17 +0100 on 21 May (1305976662), James Harper wrote:
> > 
> > On 21/05/2011 10:41, "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
> wrote:
> > 
> > > I think I asked this a while back already, but is it possible to map
> the
> > > same page of memory to multiple pfn's in a HVM DomU? That would
> resolve
> > > the problems that occur when Windows hibernates my ballooned out
> > > memory...
> > 
> > I'm pretty sure it's not currently possible, but might not be hard to
> add
> > support for it. Tim will know better than me.
> > 
> I think that was the answer last time :)

The memory-sharing code would allow this, AFAICS, but it's not
super-mature just yet, and it relies on being able to undo the sharing
on writes, which defeats the purpose of ballooning. 

Since I'm already tinkering in the p2m code I can look into it again.
Just allowing aliasing will break live migration (and probably
save/restore) since there's no easy way for the dom0 tools to know which
frames alias each other and all the accesses are done by PFN.

Is there no way to intercept this on the driver side?  I think I mean:
are you writing out whole frames or does Windows compress them first?


Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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