On Wed, 2008-03-12 at 09:19 -0700, Jeremy Fitzhardinge wrote:
quoted text
> Martin Schwidefsky wrote:
> > The state transitions (a diagram would be nicer but that is too hard
> > to do in ascii art...):
> > {Ur,Sr,Vr,Pr}: a resident page will change its block usage state if the
> >      guest requests it with page_set_{unused,stable,volatile}.
> > {Uz,Sz,Vz}: a logically zero page will change its block usage state if the
> >      guest requests it with page_set_{unused,stable,volatile}. The
> >      guest can't create the Pz state, the state will be Vz instead.
> > Ur -> Uz: the host system can remove an unused, resident page from memory
> > Sz -> Sr: on first access a stable, logically zero page will become resident
> > Sr -> Sp: the host system can swap a stable page to disk
> > Sp -> Sr: a guest access to a Sp page forces the host to retrieve it
> > Vr -> Vz: the host can discard a volatile page
> > Sp -> Uz: a page preserved by the host will be removed if the guest sets 
> >      the block usage state to unused.
> > Sp -> Vz: a page preserved by the host will be discarded if the guest sets
> >      the block usage state to volatile.
> > Pr -> Sp: the host can move a page from Pr to Sp if it discovers that the
> >      page is dirty while trying to discard the page. The page content is
> >      written to the paging device.
> > Pr -> Vz: the host can discard a Pr page. The Pz state is replaced by the
> >      Vz state.
> 
> I created the attached .dot graph based purely on this description.  It 
> looks reasonable, but I didn't see how a page enters a Pr state.

That is the first block of state transitions: {Ur,Sr,Vr,Pr}
You can go from any of the four states to any of the remaining three.

-- 
blue skies,
  Martin.

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


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