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    SubjectRe: [PATCH 0/8] perf: add ability to sample physical data addresses
    On Tue, Jul 30, 2013 at 10:02:01AM +0200, Stephane Eranian wrote:
    > > Ahh. We don't put the useful bits in the mmap event; we'll need to fix
    > > that too then ;-)
    > >
    > > Doing so is going to be a bit of a bother since we use the tail of
    > > PERF_RECORD_MMAP for filenames and thus aren't particularly extensible.
    > >
    > > This would mean doing something like PERF_RECORD_MMAP2 and some means
    > > for userspace to requrest the new events instead of the old one.
    > >
    > Tracking mmaps even for shmat() won't cover the paging cases. When you page a
    > page back in, it most likely gets a different physical page. How would
    > we track that
    > case too using the same approach?

    It doesn't matter. Even if a page ends up being a different physical
    page, it will always be the same sb:inode:pgoffset. You should be able
    to always uniquely identify a (shared) page by that triplet.

    So if we create a net MMAP record that includes the device (substitute
    for the superblock) and inode information we should be good.


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