linux-kernel - RE: [PATCH] mm/page-writeback.c: fix sparse warnings

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Date:	Fri, 17 Apr 2009 14:01:20 -0400
From:	"H Hartley Sweeten" <hartleys@...ionengravers.com>
To:	"Johannes Weiner" <hannes@...xchg.org>
Cc:	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] mm/page-writeback.c: fix sparse warnings

On Thursday, April 16, 2009 10:28 PM, Johannes Weiner wrote:
> On Thu, Apr 16, 2009 at 09:26:35PM -0400, H Hartley Sweeten wrote:
>> Fix two sparse warnings in mm/page-writeback.c.
>
> You fixed code rather than warnings, right? ;)

Correct. I should have used a different subject...

>> get_dirty_limits() calls clip_bdi_dirty_limit() and
task_dirty_limit()
>> with variable pbdi_dirty as one of the arguments. This variable is
>> an unsigned long * but both functions expect it to be a long *. This
>> causes the following sparse warnings:
>> 
>>   warning: incorrect type in argument 3 (different signedness)
>>      expected long *pbdi_dirty
>>      got unsigned long *pbdi_dirty
>>   warning: incorrect type in argument 2 (different signedness)
>>      expected long *pdirty
>>      got unsigned long *pbdi_dirty
>> 
>> Fix the warnings by changing the long * to unsigned long * in both
>> functions.
>> 
>> Signed-off-by: H Hartley Sweeten <hsweeten@...ionengravers.com>
>> 
>> ---
>> 
>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
>> index 30351f0..e40b3e3 100644
>> --- a/mm/page-writeback.c
>> +++ b/mm/page-writeback.c
>> @@ -265,18 +265,20 @@ static void bdi_writeout_fraction(struct
>> backing_dev_info *bdi,
>>   * This avoids exceeding the total dirty_limit when the floating
>> averages
>>   * fluctuate too quickly.
>>   */
>> -static void
>> -clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long
>> *pbdi_dirty)
>
> Your patches wrap, please fix your mail client to not do this.

Sorry about that. As far as I can tell, wrap occurs when my email
provider
bounces the message. I'm working on trying to get it resolved.

>> +static void clip_bdi_dirty_limit(struct backing_dev_info *bdi,
>> +		unsigned long dirty, unsigned long *pbdi_dirty)
>>  {
>> -	long avail_dirty;
>> +	unsigned long avail_dirty;
>> +	unsigned long nr_pages;
>>  
>> -	avail_dirty = dirty -
>> -		(global_page_state(NR_FILE_DIRTY) +
>> +	nr_pages = global_page_state(NR_FILE_DIRTY) +
>>  		 global_page_state(NR_WRITEBACK) +
>>  		 global_page_state(NR_UNSTABLE_NFS) +
>> -		 global_page_state(NR_WRITEBACK_TEMP));
>> +		 global_page_state(NR_WRITEBACK_TEMP);
>>  
>> -	if (avail_dirty < 0)
>> +	if (nr_pages < dirty)
>> +		avail_dirty = dirty - nr_pages;
>> +	else
>>  		avail_dirty = 0;
>
> No need for a new variable, especially if nr_pages really counts
> available dirty pages.
>
>	avail_dirty = global_page_state() + ...
>	if (avail_dirty < dirty)
>		avail_dirty = dirty - avail_dirty;
>	else
>		avail_dirty = 0;
>
> Hm?

True. Didn't think about that.

I will update the patch and resubmit. Unfortunately it will wrap again.
;-)

Regards,
Hartley
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