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    SubjectRe: [PATCH v4 3/3] KVM: x86/mmu: Add detailed page size stats
    Hi Peter,


    On Wed, Aug 11, 2021 at 6:12 AM Peter Xu <peterx@redhat.com> wrote:
    >
    > On Tue, Aug 10, 2021 at 06:06:51PM -0700, Mingwei Zhang wrote:
    > > Regarding the pursuit for accuracy, I think there might be several
    > > reasons. One of the most critical reasons that I know is that we need
    > > to ensure dirty logging works correctly, i.e., when dirty logging is
    > > enabled, all huge pages (both 2MB and 1GB) _are_ gone. Hope that
    > > clarifies a little bit?
    >
    > It's just for statistics, right? I mean dirty log should be working even
    > without this change.

    That's true. What I meant was that the accurate stats might be able to
    help verifying a property of dirty logging as a side benefit. Sorry
    for the confusion.

    >
    > But I didn't read closely last night, so we want to have "how many huge pages
    > we're mapping", not "how many we've mapped in the history". Yes that makes
    > sense to be accurate. I should have looked more carefully, sorry.
    >
    > PS: it turns out atomic is not that expensive as I thought even on a 200 core
    > system, which takes 7ns (but for sure it's still expensive than normal memory
    > ops, and bus locking); I thought it'll be bigger as on a 40 core system I got
    > 15ns which is 2x of my laptop of 8 cores, but it didn't really grow but shrink.

    Thanks for the information about atomic access!
    >
    > Thanks,
    >
    > --
    > Peter Xu
    >

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