On Wed, 2008-03-12 at 13:45 -0700, Jeremy Fitzhardinge wrote: > Vp should never happen, since you'd never preserve a V page. And surely > it would be Pr -> Sr, since the hypervisor wouldn't push the page to > backing store when you change the client state.
Vp does not happen in the current implementation. But it actually may be useful. z/VM has multiple layers of paging, the first goes to expanded storage which is very fast. If you make the page Vz and the guests needs it you have to do a standard Linux I/O to get retrieve the page. This can be slower than a read and a write to expanded storage. > > 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. > > Well, you implicitly see the hypervisor state. If you touch a [UV]z > page then you get a fault telling you that the page has been taken away > from you (I think). And it would definitely help with debugging (seems > likely there's lots of scope for race conditions if you prematurely tell > the hypervisor you don't need the page any more...). You get an addressing exception if you touch a Uz page. This indicates a BUG in the Linux code because this is a use after free. If the guests touches a Vz page you get a discard fault. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. _______________________________________________ Virtualization mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/virtualization
