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    SubjectRe: [PATCH 4/5] always lock the root (oldest) anon_vma
    On Wed, 26 May 2010 15:40:44 -0400
    Rik van Riel <riel@redhat.com> wrote:

    > Subject: always lock the root (oldest) anon_vma
    >
    > Always (and only) lock the root (oldest) anon_vma whenever we do something in an
    > anon_vma. The recently introduced anon_vma scalability is due to the rmap code
    > scanning only the VMAs that need to be scanned. Many common operations still
    > took the anon_vma lock on the root anon_vma, so always taking that lock is not
    > expected to introduce any scalability issues.
    >
    > However, always taking the same lock does mean we only need to take one lock,
    > which means rmap_walk on pages from any anon_vma in the vma is excluded from
    > occurring during an munmap, expand_stack or other operation that needs to
    > exclude rmap_walk and similar functions.
    >
    > Also add the proper locking to vma_adjust.
    >
    > Signed-off-by: Rik van Riel <riel@redhat.com>

    Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>





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