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    SubjectRe: [patch 6/6] Guest page hinting: s390 support.
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    On Wed, 2008-03-12 at 09:19 -0700, Jeremy Fitzhardinge wrote:
    > 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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