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rmap: move exclusively owned pages to own anon_vma in do_wp_page()

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When the parent process breaks the COW on a page, both the original which
is mapped at child and the new page which is mapped parent end up in that
same anon_vma.  Generally this won't be a problem, but for some workloads
it could preserve the O(N) rmap scanning complexity.

A simple fix is to ensure that, when a page which is mapped child gets
reused in do_wp_page, because we already are the exclusive owner, the page
gets moved to our own exclusive child's anon_vma.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rik van Riel
2010-03-05 13:42:09 -08:00
committed by Linus Torvalds
parent 033a64b56a
commit c44b674323
3 changed files with 32 additions and 0 deletions
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7
mm/memory.c
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@@ -2138,6 +2138,13 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
page_cache_release(old_page);
}
reuse = reuse_swap_page(old_page);
if (reuse)
/*
* The page is all ours. Move it to our anon_vma so
* the rmap code will not search our parent or siblings.
* Protected against the rmap code by the page lock.
*/
page_move_anon_rmap(old_page, vma, address);
unlock_page(old_page);
} else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
(VM_WRITE|VM_SHARED))) {