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    SubjectRe: [PATCH 1/2] Report the pagesize backing a VMA in /proc/pid/smaps
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    On Wed, 2008-09-24 at 20:11 +0100, Mel Gorman wrote:
    > I don't get what you mean by it being sprinkled in each smaps file. How
    > would you present the data?

    1. figure out what the file path is from smaps
    2. look up the mount
    3. look up the page sizes from the mount's information

    > > We should be able to figure out which
    > > mount the file is from and, from there, maybe we need some per-mount
    > > information exported.
    >
    > Per-mount information is already exported and you can infer the data about
    > huge pagesizes. For example, if you know the default huge pagesize (from
    > /proc/meminfo), and the file is on hugetlbfs (read maps, then /proc/mounts)
    > and there is no pagesize= mount option (mounts again), you could guess what the
    > hugepage that is backing a VMA is. Shared memory segments are a little harder
    > but again, you can infer the information if you look around for long enough.
    >
    > However, this is awkward and not very user-friendly. With the patches (minus
    > MMUPageSize as I think we've agreed to postpone that), it's easy to see what
    > pagesize is being used at a glance. Without it, you need to know a fair bit
    > about hugepages are implemented in Linux to infer the information correctly.

    I agree completely. But, if we consider this a user ABI thing, then
    we're stuck with it for a long time, and we better make it flexible
    enough to at least contain the gunk we're planning on adding in a small
    number of years, like the fallback. We don't want to be adding this
    stuff if it isn't going to be stable.

    -- Dave



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