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[PATCH] mm: micro-optimise rmap

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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: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Nick Piggin 2005-09-03 15:54:47 -07:00 • committed by Linus Torvalds
parent c3dce2d89c
commit 2822c1aa57
1 changed files with 11 additions and 10 deletions
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15
mm/rmap.c
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@ -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 */