tree b722f3c6fa28d1228e34adbcb85fee8683b34069
parent e20e87795834f2f14cb53baf657b91d9c39f92c8
author Steven Rostedt <srostedt@redhat.com> 1294962378 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> 1294968756 -0800

mm: remove likely() from grab_cache_page_write_begin()

Running the annotated branch profiler on a box doing average work
(firefox, evolution, xchat, distcc farm), the likely() used in
grab_cache_page_write_begin() was incorrect most of the time:

 correct incorrect  %        Function                  File              Line
 ------- ---------  -        --------                  ----              ----
 1924262 71332401  97 grab_cache_page_write_begin    filemap.c           2206

Adding a trace_printk() and running the function tracer limited to
just this function I can see:

        gconfd-2-2696  [000]  4467.268935: grab_cache_page_write_begin: page=          (null) mapping=ffff8800676a9460 index=7
        gconfd-2-2696  [000]  4467.268946: grab_cache_page_write_begin <-ext3_write_begin
        gconfd-2-2696  [000]  4467.268947: grab_cache_page_write_begin: page=          (null) mapping=ffff8800676a9460 index=8
        gconfd-2-2696  [000]  4467.268959: grab_cache_page_write_begin <-ext3_write_begin
        gconfd-2-2696  [000]  4467.268960: grab_cache_page_write_begin: page=          (null) mapping=ffff8800676a9460 index=9
        gconfd-2-2696  [000]  4467.268972: grab_cache_page_write_begin <-ext3_write_begin
        gconfd-2-2696  [000]  4467.268973: grab_cache_page_write_begin: page=          (null) mapping=ffff8800676a9460 index=10
        gconfd-2-2696  [000]  4467.268991: grab_cache_page_write_begin <-ext3_write_begin
        gconfd-2-2696  [000]  4467.268992: grab_cache_page_write_begin: page=          (null) mapping=ffff8800676a9460 index=11
        gconfd-2-2696  [000]  4467.269005: grab_cache_page_write_begin <-ext3_write_begin

Which shows that a lot of calls from ext3_write_begin will result in the
page returned by "find_lock_page" will be NULL.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Nick Piggin <npiggin@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>