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    SubjectRe: [PATCH] mm: munlock use mapcount to avoid terrible overhead
    On Tue, 18 Oct 2011, Andrew Morton wrote:
    > On Tue, 18 Oct 2011 17:02:56 -0700 (PDT)
    > Hugh Dickins <hughd@google.com> wrote:
    >
    > > A process spent 30 minutes exiting, just munlocking the pages of a large
    > > anonymous area that had been alternately mprotected into page-sized vmas:
    > > for every single page there's an anon_vma walk through all the other
    > > little vmas to find the right one.
    >
    > And how long did the test case take with the patch applied?

    5 seconds in the case tried; but the issue is quadratic,
    so you can make the improvement look arbitrarily good.

    Hugh


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