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    SubjectRe: [PATCH 1/8] mm: munlock use follow_page
    From
    2009/9/8 Hugh Dickins <hugh.dickins@tiscali.co.uk>:
    > Hiroaki Wakabayashi points out that when mlock() has been interrupted
    > by SIGKILL, the subsequent munlock() takes unnecessarily long because
    > its use of __get_user_pages() insists on faulting in all the pages
    > which mlock() never reached.
    >
    > It's worse than slowness if mlock() is terminated by Out Of Memory kill:
    > the munlock_vma_pages_all() in exit_mmap() insists on faulting in all the
    > pages which mlock() could not find memory for; so innocent bystanders are
    > killed too, and perhaps the system hangs.
    >
    > __get_user_pages() does a lot that's silly for munlock(): so remove the
    > munlock option from __mlock_vma_pages_range(), and use a simple loop of
    > follow_page()s in munlock_vma_pages_range() instead; ignoring absent
    > pages, and not marking present pages as accessed or dirty.
    >
    > (Change munlock() to only go so far as mlock() reached?  That does not
    > work out, given the convention that mlock() claims complete success even
    > when it has to give up early - in part so that an underlying file can be
    > extended later, and those pages locked which earlier would give SIGBUS.)
    >
    > Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>

    Reviewed-by: Hiroaki Wakabayashi <primulaelatior@gmail.com>

    It very simple and so cool! I have learned something.

    --
    Thanks,
    Hiroaki Wakabayashi
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