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    SubjectRe: [PATCH 01/12] mm,migration: Take a reference to the anon_vma before migrating
    On Fri, Feb 19, 2010 at 09:12:44AM +0900, KAMEZAWA Hiroyuki wrote:
    > On Thu, 18 Feb 2010 18:02:31 +0000
    > Mel Gorman <> wrote:
    > > rmap_walk_anon() does not use page_lock_anon_vma() for looking up and
    > > locking an anon_vma and it does not appear to have sufficient locking to
    > > ensure the anon_vma does not disappear from under it.
    > >
    > > This patch copies an approach used by KSM to take a reference on the
    > > anon_vma while pages are being migrated. This should prevent rmap_walk()
    > > running into nasty surprises later because anon_vma has been freed.
    > >
    > > Signed-off-by: Mel Gorman <>
    > I have no objection to this direction. But after this patch, you can remove
    > rcu_read_lock()/unlock() in unmap_and_move().
    > ruc_read_lock() is for guarding against anon_vma replacement.

    Thanks. I expected that would be the case but was going to leave at
    least one kernel release between when compaction went in and I did that.

    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab

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