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Commit 2822c1aa authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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[PATCH] mm: micro-optimise rmap 



Microoptimise page_add_anon_rmap.  Although these expressions are used only in
the taken branch of the if() statement, the compiler can't reorder them inside
because atomic_inc_and_test is a barrier.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent c3dce2d8

mm/rmap.c

+11 −10
Original line number Original line Diff line number Diff line
@@ -439,22 +439,23 @@ int page_referenced(struct page *page, int is_locked, int ignore_token) 
void page_add_anon_rmap(struct page *page,

void page_add_anon_rmap(struct page *page,

	struct vm_area_struct *vma, unsigned long address)

	struct vm_area_struct *vma, unsigned long address)

{

{

	struct anon_vma *anon_vma = vma->anon_vma;

	pgoff_t index;



	BUG_ON(PageReserved(page));

	BUG_ON(PageReserved(page));

	BUG_ON(!anon_vma);





	inc_mm_counter(vma->vm_mm, anon_rss);

	inc_mm_counter(vma->vm_mm, anon_rss);





	if (atomic_inc_and_test(&page->_mapcount)) {

		struct anon_vma *anon_vma = vma->anon_vma;

		pgoff_t index;



		BUG_ON(!anon_vma);

		anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;

		anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;

		page->mapping = (struct address_space *) anon_vma;



		index = (address - vma->vm_start) >> PAGE_SHIFT;

		index = (address - vma->vm_start) >> PAGE_SHIFT;

		index += vma->vm_pgoff;

		index += vma->vm_pgoff;

		index >>= PAGE_CACHE_SHIFT - PAGE_SHIFT;

		index >>= PAGE_CACHE_SHIFT - PAGE_SHIFT;



	if (atomic_inc_and_test(&page->_mapcount)) {

		page->index = index;

		page->index = index;

		page->mapping = (struct address_space *) anon_vma;



		inc_page_state(nr_mapped);

		inc_page_state(nr_mapped);

	}

	}

	/* else checking page index and mapping is racy */

	/* else checking page index and mapping is racy */