[Xen-devel] Re: super page with live migration

["Zhai, Edwin" <edwin.zhai@xxxxxxxxx>]

Keir Fraser wrote:
> On 26/9/08 08:45, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx> wrote:
>
>   
> > As you know, we try to allocate super pages in xc_hvm_build for better
> > performance in EPT case. But the same logic is missing in xc_domain_restore.
> >
> > When try to add the logic, I found it is blocked by the lazy populate
> > algorithm 
> > in restore -- only populating the pages received from source side rather than
> > doing it at one time.
> >
> > So the result is the EPT guest has performance drop after live migration:(
> >
> > Do you have any plan to change the lazy populate algorithm? The purpose of it,
> > I 
> > believe, is to make restore process work without guest memory layout
> > knowledge.  
> >     
> Yes: If pseudo-phys page is not yet populated in target domain, AND it is
> first page of a 2MB extent, AND no other pages in that extent are yet
> populated, AND the next pages in the save-image stream populate that extent
> in order, THEN allocate a superpage. This is made trickier by the fact that
> the next 511 pages (to make the 2MB extent) might be split across a batch
> boundary. So we'll have to optimistically allocate a superpage in that case,
> and then shatter it if it turns out that the contiguous stream of
> pseudo-phys addresses is broken in the next batch.
>   
It's really tricky logic, and may make the migration process longer:(

Maybe the flag the start-of-a-superpage as Tim said can make it easier.



Thanks,


>  -- Keir
>
>
>   
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