Re: [RFC][PATCH 05/10] mm: Remove likely() from grab_cache_page_write_begin()

Nick Piggin
2010-12-07T06:57:07Z

On Mon, Dec 06, 2010 at 09:24:10PM -0500, Steven Rostedt wrote:
> [ Resending to Nick's real email address ]
>
> From: Steven Rostedt <srostedt@redhat.com>
>
> 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.
>
> Cc: Nick Piggin <npiggin@kernel.dk>

Looks good,

Acked-by: Nick Piggin <npiggin@kernel.dk>