linux-kernel - Re: [PATCH] iomap: skip unnecessary ifs_block_is

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Message-ID: <75EE8C762B61A1E0+70ff3f7f-2ddd-4109-ac57-d395a69302f3@uniontech.com>
Date: Thu, 10 Apr 2025 13:37:42 +0800
From: Gou Hao <gouhao@...ontech.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: brauner@...nel.org, linux-xfs@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 wangyuli@...ontech.com, gouhaojake@....com
Subject: Re: [PATCH] iomap: skip unnecessary ifs_block_is_uptodate check


On 2025/4/9 23:30, Darrick J. Wong wrote:
> On Wed, Apr 09, 2025 at 01:29:24AM +0800, Gou Hao wrote:
>> After the first 'for' loop, the first call to
>> ifs_block_is_uptodate always evaluates to 0.
>>
>> Signed-off-by: Gou Hao <gouhao@...ontech.com>
>> ---
>>   fs/iomap/buffered-io.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
>> index 31553372b33a..2f52e8e61240 100644
>> --- a/fs/iomap/buffered-io.c
>> +++ b/fs/iomap/buffered-io.c
>> @@ -259,7 +259,7 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
>>   		}
>>   
>>   		/* truncate len if we find any trailing uptodate block(s) */
>> -		for ( ; i <= last; i++) {
>> +		for (i++; i <= last; i++) {
> Hmmm... prior to the loop, $i is either the first !uptodate block, or
> it's past $last.  Assuming there's no overflow (there's no combination
> of huge folios and tiny blksize that I can think of) then yeah, there's
> no point in retesting that the same block $i is uptodate since we hold
> the folio lock so nobody else could have set uptodate.
>
> Reviewed-by: "Darrick J. Wong" <djwong@...nel.org>
>
> --D

Thank you for your review. The explanation is very clear. I will revise the

commit message and send the V2 patch.

--

thanks,

Gou Hao

>
>>   			if (ifs_block_is_uptodate(ifs, i)) {
>>   				plen -= (last - i + 1) * block_size;
>>   				last = i - 1;
>> -- 
>> 2.20.1
>>
>>