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| author | Steven Rostedt <srostedt@redhat.com> | 2011-01-14 02:46:16 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-01-14 04:32:36 +0300 |
| commit | 088e54658f559a13c2b988086512d76fe9e8f846 (patch) | |
| tree | 35a5e0f82186dfa740751ec33f2fcdd90e347b0b | |
| parent | ddf9c6d472825ceda66b3adff0f6437dbcd37f71 (diff) | |
| download | linux-088e54658f559a13c2b988086512d76fe9e8f846.tar.xz | |
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>
| -rw-r--r-- | include/linux/pagemap.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 2d1ffe3cf1ee..9c66e994540f 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; } |