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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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1
include/linux/rmap.h
View file

@ -125,6 +125,7 @@ static inline void anon_vma_merge(struct vm_area_struct *vma,
/*
* rmap interfaces called when adding or removing pte of page
*/
void page_move_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
void page_add_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
void page_add_new_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
void page_add_file_rmap(struct page *);

7
mm/memory.c
View file

@ -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))) {

24
mm/rmap.c
View file

@ -715,6 +715,30 @@ 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