On Wed, 2008-03-12 at 15:04 -0500, Anthony Liguori wrote:
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> Jeremy Fitzhardinge wrote:
> >> With stable_if_clean you are refering to stable_if_present?
> > 
> > No.  I misunderstood and thought that stable_if_present sets the Px 
> > state.  I'd overlooked the writable flag on page_set_volatile().
> > 
> >>  If yes the
> >> answer is that this operation is used to get a page from Vx/Px back to
> >> Sx but only if the page has not been discarded.
> > 
> > So you mean it will change Vr/Pr to Sr but everything else will fail?  

In the extended version Vp/Pp to Sr as well but the current z/VM code
will discard a page if the host picks a Vr/Pr page to swap it.

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> Well presumably Vp/Pr => Sp?  Is is true that from the guest's 
> perspective, all of the 'p' states are identical to the 'r' states?

Basically yes. The guest doesn't care about the host state.

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> Do the host states even really need visibility to the guest at all?  It 
> may be useful for the guest to be able to distinguish between Ur and Uz 
> but it doesn't seem necessary.

It is very useful for debugging to have the host state in the guest as
well. There is one possible optimization: if the guests finds a Uz page
in the free list, it can make it Sz and doesn't have to clear it because
the host will provide an already empty page (not yet implemented
though).

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> BTW Jeremy, the .dot was very useful!

I've search on my disk and found the state diagrams we've used for the
OLS paper. You may find these useful as well.

-- 
blue skies,
  Martin.

"Reality continues to ruin my life." - Calvin.