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    SubjectRe: [RFC][PATCH 1/6] count transparent hugepage splits
    On Mon, 31 Jan 2011, Dave Hansen wrote:

    > The khugepaged process collapses transparent hugepages for us. Whenever
    > it collapses a page into a transparent hugepage, we increment a nice
    > global counter exported in sysfs:
    > /sys/kernel/mm/transparent_hugepage/khugepaged/pages_collapsed
    > But, transparent hugepages also get broken down in quite a few
    > places in the kernel. We do not have a good idea how how many of
    > those collpased pages are "new" versus how many are just fixing up
    > spots that got split a moment before.
    > Note: "splits" and "collapses" are opposites in this context.
    > This patch adds a new sysfs file:
    > /sys/kernel/mm/transparent_hugepage/pages_split
    > It is global, like "pages_collapsed", and is incremented whenever any
    > transparent hugepage on the system has been broken down in to normal
    > PAGE_SIZE base pages. This way, we can get an idea how well khugepaged
    > is keeping up collapsing pages that have been split.
    > I put it under /sys/kernel/mm/transparent_hugepage/ instead of the
    > khugepaged/ directory since it is not strictly related to
    > khugepaged; it can get incremented on pages other than those
    > collapsed by khugepaged.
    > The variable storing this is a plain integer. I needs the same
    > amount of locking that 'khugepaged_pages_collapsed' has, for
    > instance.

    i.e. no global locking, but we've accepted the occassional off-by-one
    error (even though splitting of hugepages isn't by any means lightning
    fast and the overhead of atomic ops would be negligible).

    > Signed-off-by: Dave Hansen <>

    Acked-by: David Rientjes <>

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      Last update: 2011-02-03 22:25    [W:0.022 / U:242.012 seconds]
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