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authorRik van Riel <riel@redhat.com>2010-03-05 13:42:09 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-03-06 11:26:26 -0800
commitc44b674323f4a2480dbeb65d4b487fa5f06f49e0 (patch)
treeb753050e6752eb2fc961ad3ea5dfdf88ef88364d /mm
parent033a64b56aed798991de18d226085dfb1ccd858d (diff)
downloadconfigs-c44b674323f4a2480dbeb65d4b487fa5f06f49e0.tar.gz
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.c7
-rw-r--r--mm/rmap.c24
2 files changed, 31 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c
index dc785b438d7..d1153e37e9b 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 23ecd0a892d..28bcdc433d8 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