Re: [RESEND PATCH] fs/buffer.c: exit if already confirmed page has dirty and writeback buffers

[Gu Zheng <guz.fnst@cn.fujitsu.com>]

Hi Jan,

On 11/07/2013 07:44 PM, Jan Kara wrote:

> On Tue 05-11-13 18:02:03, Gu Zheng wrote:
>> Stop the loop of iterating bh if we have confirmed page
>> has dirty and writeback buffers.
>   Thanks for the patch. What I'm somewhat missing here is a motivation of
> the patch. For the common case where blocksize == pagesize this is a noop
> (only adds some code). 

Yes, you're right.

> For the case where blocksize < pagesize we can
> possibly save checking some buffers but how common is that going be?

It's really hard to say.:( But many file systems support small blocksize.

> Does that minimal speed up outweight the cost of additional check / code
> complication?

In fact, without complete test. But I think the speed up can outweigh the cost
if blocksize small enough. For example, blocksize: 1k, pagesize: 4k, we can
reduce 6 bh check(3 dirty, 3 writeback) in the best case.

Best regards,
Gu

> 
> 								Honza
> 
>>
>> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
>> ---
>>  fs/buffer.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/buffer.c b/fs/buffer.c
>> index 6024877..519cc5c 100644
>> --- a/fs/buffer.c
>> +++ b/fs/buffer.c
>> @@ -112,7 +112,7 @@ void buffer_check_dirty_writeback(struct page *page,
>>  			*dirty = true;
>>  
>>  		bh = bh->b_this_page;
>> -	} while (bh != head);
>> +	} while ((bh != head) && !(*writeback && *dirty));
>>  }
>>  EXPORT_SYMBOL(buffer_check_dirty_writeback);
>>  
>> -- 
>> 1.7.7
>>
>> --
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