diff options
| author |   Christoph Lameter <clameter@sgi.com> | 2007-05-06 14:49:40 -0700 |
|---|---|---|
| committer |   Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-05-07 12:12:53 -0700 |
| commit | 6d7779538f765963ced45a3fa4bed7ba8d2c277d (patch) | |
| tree | 07d47e6ff1ab30309004e2ba0674dcabd83945c1 /include/linux/mm.h | |
| parent | Make page->private usable in compound pages (diff) | |
| download | linux-dev-6d7779538f765963ced45a3fa4bed7ba8d2c277d.tar.xz linux-dev-6d7779538f765963ced45a3fa4bed7ba8d2c277d.zip | |
mm: optimize compound_head() by avoiding a shared page flag
The patch adds PageTail(page) and PageHead(page) to check if a page is the
head or the tail of a compound page. This is done by masking the two bits
describing the state of a compound page and then comparing them. So one
comparision and a branch instead of two bit checks and two branches.
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/mm.h')
| -rw-r--r-- | include/linux/mm.h | 11 |
1 files changed, 2 insertions, 9 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index 8c149fa4491d..695b90437bbc 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -269,14 +269,7 @@ static inline int get_page_unless_zero(struct page *page) static inline struct page *compound_head(struct page *page) { - /* - * We could avoid the PageCompound(page) check if - * we would not overload PageTail(). - * - * This check has to be done in several performance critical - * paths of the slab etc. IMHO PageTail deserves its own flag. - */ - if (unlikely(PageCompound(page) && PageTail(page))) + if (unlikely(PageTail(page))) return page->first_page; return page; } @@ -327,7 +320,7 @@ static inline compound_page_dtor *get_compound_page_dtor(struct page *page) static inline int compound_order(struct page *page) { - if (!PageCompound(page) || PageTail(page)) + if (!PageHead(page)) return 0; return (unsigned long)page[1].lru.prev; } |