From 6d7779538f765963ced45a3fa4bed7ba8d2c277d Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Sun, 6 May 2007 14:49:40 -0700 Subject: 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 Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'mm') diff --git a/mm/page_alloc.c b/mm/page_alloc.c index fc241fe295a..36d713e216e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -235,12 +235,11 @@ static void prep_compound_page(struct page *page, unsigned long order) set_compound_page_dtor(page, free_compound_page); set_compound_order(page, order); - __SetPageCompound(page); + __SetPageHead(page); for (i = 1; i < nr_pages; i++) { struct page *p = page + i; __SetPageTail(p); - __SetPageCompound(p); p->first_page = page; } } @@ -253,17 +252,16 @@ static void destroy_compound_page(struct page *page, unsigned long order) if (unlikely(compound_order(page) != order)) bad_page(page); - if (unlikely(!PageCompound(page))) + if (unlikely(!PageHead(page))) bad_page(page); - __ClearPageCompound(page); + __ClearPageHead(page); for (i = 1; i < nr_pages; i++) { struct page *p = page + i; - if (unlikely(!PageCompound(p) | !PageTail(p) | + if (unlikely(!PageTail(p) | (p->first_page != page))) bad_page(page); __ClearPageTail(p); - __ClearPageCompound(p); } } -- cgit v1.2.3-70-g09d2