• Steven Rostedt's avatar
    mm: remove likely() from grab_cache_page_write_begin() · c585a267
    Steven Rostedt authored
    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: default avatarSteven Rostedt <rostedt@goodmis.org>
    Acked-by: default avatarNick Piggin <npiggin@kernel.dk>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    c585a267
filemap.c 66.7 KB