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Commit c44b6743 authored by Rik van Riel's avatar Rik van Riel Committed by Linus Torvalds
Browse files

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: default avatarRik 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: default avatarMinchan Kim <minchan.kim@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 033a64b5

include/linux/rmap.h

+1 −0
Original line number Diff line number Diff line
@@ -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 *);

mm/memory.c

+7 −0
Original line number Diff line number Diff line
@@ -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))) {

mm/rmap.c

+24 −0
Original line number Diff line number Diff line
@@ -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