diff options
| author | Rik van Riel <riel@redhat.com> | 2010-03-05 13:42:09 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-03-06 11:26:26 -0800 |
| commit | c44b674323f4a2480dbeb65d4b487fa5f06f49e0 (patch) | |
| tree | b753050e6752eb2fc961ad3ea5dfdf88ef88364d /mm | |
| parent | 033a64b56aed798991de18d226085dfb1ccd858d (diff) | |
| download | linux-c44b674323f4a2480dbeb65d4b487fa5f06f49e0.tar.bz2 | |
rmap: move exclusively owned pages to own anon_vma in do_wp_page()
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>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/memory.c | 7 | ||||
| -rw-r--r-- | mm/rmap.c | 24 |
2 files changed, 31 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c index dc785b438d70..d1153e37e9ba 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -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))) { diff --git a/mm/rmap.c b/mm/rmap.c index 23ecd0a892df..28bcdc433d88 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -716,6 +716,30 @@ int page_mkclean(struct page *page) EXPORT_SYMBOL_GPL(page_mkclean); /** + * page_move_anon_rmap - move a page to our anon_vma + * @page: the page to move to our anon_vma + * @vma: the vma the page belongs to + * @address: the user virtual address mapped + * + * When a page belongs exclusively to one process after a COW event, + * that page can be moved into the anon_vma that belongs to just that + * process, so the rmap code will not search the parent or sibling + * processes. + */ +void page_move_anon_rmap(struct page *page, + struct vm_area_struct *vma, unsigned long address) +{ + struct anon_vma *anon_vma = vma->anon_vma; + + VM_BUG_ON(!PageLocked(page)); + VM_BUG_ON(!anon_vma); + VM_BUG_ON(page->index != linear_page_index(vma, address)); + + anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; + page->mapping = (struct address_space *) anon_vma; +} + +/** * __page_set_anon_rmap - setup new anonymous rmap * @page: the page to add the mapping to * @vma: the vm area in which the mapping is added |