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authorSteven Rostedt <srostedt@redhat.com>2011-01-13 15:46:16 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-13 17:32:36 -0800
commit088e54658f559a13c2b988086512d76fe9e8f846 (patch)
tree35a5e0f82186dfa740751ec33f2fcdd90e347b0b /include/linux/pagemap.h
parentddf9c6d472825ceda66b3adff0f6437dbcd37f71 (diff)
mm: remove likely() from mapping_unevictable()
The mapping_unevictable() has a likely() around the mapping parameter. This mapping parameter comes from page_mapping() which has an unlikely() that the page will be set as PAGE_MAPPING_ANON, and if so, it will return NULL. One would think that this unlikely() means that the mapping returned by page_mapping() would not be NULL, but where page_mapping() is used just above mapping_unevictable(), that unlikely() is incorrect most of the time. This means that the "likely(mapping)" in mapping_unevictable() is incorrect most of the time. Running the annotated branch profiler on my main box which runs firefox, evolution, xchat and is part of my distcc farm, I had this: correct incorrect % Function File Line ------- --------- - -------- ---- ---- 12872836 1269443893 98 mapping_unevictable pagemap.h 51 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 mapping_unevictable() is also a static inline but seems to be used only once in my setup. The unlikely in page_mapping() was correct a total of 1909540379 times and incorrect 1270533123 times, with a 39% being incorrect. Perhaps this is enough to remove the unlikely from page_mapping() as well. Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: Nick Piggin <npiggin@kernel.dk> Acked-by: Rik van Riel <riel@redhat.com> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/pagemap.h')
-rw-r--r--include/linux/pagemap.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2d1ffe3cf1e..9c66e994540 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -48,7 +48,7 @@ static inline void mapping_clear_unevictable(struct address_space *mapping)
static inline int mapping_unevictable(struct address_space *mapping)
{
- if (likely(mapping))
+ if (mapping)
return test_bit(AS_UNEVICTABLE, &mapping->flags);
return !!mapping;
}