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    SubjectRe: [RFC] respect the referenced bit of KVM guest pages?
    On 08/05/2009 05:15 PM, Rik van Riel wrote:
    >> If that's indeed the case, we can have the EPT ageing mechanism give
    >> pages a bit more time around by using an available bit in the EPT
    >> PTEs to return accessed on the first pass and not-accessed on the
    >> second.
    >
    > Can we find out which pages are EPT pages?
    >

    No need to (see below).

    > If so, we could unmap them when they get moved from the
    > active to the inactive list, and soft fault them back in
    > on access, emulating the referenced bit for EPT pages and
    > making page replacement on them work like it should.

    It should be easy to implement via the mmu notifier callback: when the
    mm calls clear_flush_young(), mark it as young, and unmap it from the
    EPT pagetable.

    > Your approximation of pretending the page is accessed the
    > first time and pretending it's not the second time sounds
    > like it will just lead to less efficient FIFO replacement,
    > not to anything even vaguely approximating LRU.

    Right, it's just a hack that gives EPT pages higher priority, like the
    original patch suggested. Note that LRU for VMs is not a good
    algorithm, since the VM will also reference the least recently used
    page, leading to thrashing.

    --
    error compiling committee.c: too many arguments to function



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