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    SubjectRe: [patch 3/9] Guest page hinting: volatile page cache.
    Martin Schwidefsky wrote
    > The discard fault happens on access to a volatile that has been
    > discarded. An important property of the s390 architecture comes into
    > play here: there are two page tables, a guest page table and a host page
    > table. What the guest perceives as its "physical" memory is in virtual
    > storage for the host. An address resolution has to walk two pages
    > tables, if a pte is invalid in either table you get a fault. A guest
    > fault if the invalid pte is in the guest table and a host fault if it is
    >

    Yes, I'm familiar with that trick. Wasn't sure if you had it in
    hardware or not.

    > in the host table. That gives s390 a simple method to implement
    > discarded pages: the hypervisor just unmaps the page from the host table
    > and changes the state of the guest page. I can see that you will have a
    > much harder time to implement this on i386.
    >

    Nah, I think we'll do just fine.

    Thanks for the info - based on this, I think we can probably use the
    volatile page / swap cache changes as well for VMware, also pretty much
    unchanged. Sorry to take so long to look at these patches, BTW - I was
    on holiday for two weeks.

    Zach
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