From e20e87795834f2f14cb53baf657b91d9c39f92c8 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Thu, 13 Jan 2011 15:46:17 -0800 Subject: [PATCH] mm: remove unlikely() from page_mapping() page_mapping() has a unlikely that the mapping has PAGE_MAPPING_ANON set. But running the annotated branch profiler on a normal desktop system doing vairous tasks (xchat, evolution, firefox, distcc), it is not really that unlikely that the mapping here will have the PAGE_MAPPING_ANON flag set: correct incorrect % Function File Line ------- --------- - -------- ---- ---- 35935762 1270265395 97 page_mapping mm.h 659 1306198001 143659 0 page_mapping mm.h 657 203131478 121586 0 page_mapping mm.h 657 5415491 1116 0 page_mapping mm.h 657 74899487 1116 0 page_mapping mm.h 657 203132845 224 0 page_mapping mm.h 659 5415464 27 0 page_mapping mm.h 659 13552 0 0 page_mapping mm.h 657 13552 0 0 page_mapping mm.h 659 242630 0 0 page_mapping mm.h 657 242630 0 0 page_mapping mm.h 659 74899487 0 0 page_mapping mm.h 659 The page_mapping() is a static inline, which is why it shows up multiple times. The unlikely in page_mapping() was correct a total of 1909540379 times and incorrect 1270533123 times, with a 39% being incorrect. With this much of an error, it's best to simply remove the unlikely and have the compiler and branch prediction figure this out. Signed-off-by: Steven Rostedt Cc: KOSAKI Motohiro Cc: Nick Piggin Cc: Rik van Riel Cc: Lee Schermerhorn Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mm.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 9ade803..57e11b2 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -657,7 +657,7 @@ static inline struct address_space *page_mapping(struct page *page) VM_BUG_ON(PageSlab(page)); if (unlikely(PageSwapCache(page))) mapping = &swapper_space; - else if (unlikely((unsigned long)mapping & PAGE_MAPPING_ANON)) + else if ((unsigned long)mapping & PAGE_MAPPING_ANON) mapping = NULL; return mapping; } -- 2.7.4