[PATCH] iomap: skip unnecessary ifs_block_is_uptodate check

[PATCH] iomap: skip unnecessary ifs_block_is_uptodate check

[Gou Hao]

After the first 'for' loop, the first call to
ifs_block_is_uptodate always evaluates to 0.

Signed-off-by: Gou Hao <gouhao@uniontech.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++) {
 			if (ifs_block_is_uptodate(ifs, i)) {
 				plen -= (last - i + 1) * block_size;
 				last = i - 1;
-- 
2.20.1

Re: [PATCH] iomap: skip unnecessary ifs_block_is_uptodate check

[Darrick J. Wong]

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@uniontech.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@kernel.org>

--D


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

Re: [PATCH] iomap: skip unnecessary ifs_block_is_uptodate check

[Gou Hao]

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@uniontech.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@kernel.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
>>
>>

[PATCH V2] iomap: skip unnecessary ifs_block_is_uptodate check

[Gou Hao]

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) 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.

Signed-off-by: Gou Hao <gouhao@uniontech.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
---
 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++) {
 			if (ifs_block_is_uptodate(ifs, i)) {
 				plen -= (last - i + 1) * block_size;
 				last = i - 1;
-- 
2.20.1

Re: [PATCH V2] iomap: skip unnecessary ifs_block_is_uptodate check

[Christoph Hellwig]

On Thu, Apr 10, 2025 at 01:42:23PM +0800, Gou Hao wrote:
> 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) 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.

Capitalize the first word in the sentence and use up the 73 characters
available for the commit log:

In iomap_adjust_read_range, i is either the first !uptodate block, or it
is past last for the second loop looking for trailing uptodate blocks.
Assuming there's no overflow (there's no combination of huge folios and
tiny blksize) then yeah, there is no point in retesting that the same
block pointed to by i is uptodate since we hold the folio lock so nobody
else could have set it uptodate.

>  		/* truncate len if we find any trailing uptodate block(s) */
> -		for ( ; i <= last; i++) {
> +		for (i++; i <= last; i++) {

A bit nitpicky, but I find a i++ in the initialization condition of a
for loop a bit odd.

What about turning this into a:

		while (++i <= last) {

?

Re: [PATCH V2] iomap: skip unnecessary ifs_block_is_uptodate check

[Gou Hao]

On 2025/4/10 13:54, Christoph Hellwig wrote:
> On Thu, Apr 10, 2025 at 01:42:23PM +0800, Gou Hao wrote:
>> 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) 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.
> Capitalize the first word in the sentence and use up the 73 characters
> available for the commit log:
>
> In iomap_adjust_read_range, i is either the first !uptodate block, or it
> is past last for the second loop looking for trailing uptodate blocks.
> Assuming there's no overflow (there's no combination of huge folios and
> tiny blksize) then yeah, there is no point in retesting that the same
> block pointed to by i is uptodate since we hold the folio lock so nobody
> else could have set it uptodate.
Thank you, i will change the log in next patch.
>>   		/* truncate len if we find any trailing uptodate block(s) */
>> -		for ( ; i <= last; i++) {
>> +		for (i++; i <= last; i++) {
> A bit nitpicky, but I find a i++ in the initialization condition of a
> for loop a bit odd.
>
> What about turning this into a:
>
> 		while (++i <= last) {
>
> ?
Yes,  it is better.  I will test this.
>

[PATCH V3] iomap: skip unnecessary ifs_block_is_uptodate check

[Gou Hao]

In iomap_adjust_read_range, i is either the first !uptodate block, or it
is past last for the second loop looking for trailing uptodate blocks.
Assuming there's no overflow (there's no combination of huge folios and
tiny blksize) then yeah, there is no point in retesting that the same
block pointed to by i is uptodate since we hold the folio lock so nobody
else could have set it uptodate.

Signed-off-by: Gou Hao <gouhao@uniontech.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Suggested-by: Christoph Hellwig <hch@infradead.org>
---
 fs/iomap/buffered-io.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Changes:
V3:
- optimize commit log
- change 'for' to 'while'

V2:
- optimize commit log

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 31553372b33a..5b08bd417b28 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++) {
+		while (++i <= last) {
 			if (ifs_block_is_uptodate(ifs, i)) {
 				plen -= (last - i + 1) * block_size;
 				last = i - 1;
-- 
2.20.1

Re: [PATCH V3] iomap: skip unnecessary ifs_block_is_uptodate check

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH V3] iomap: skip unnecessary ifs_block_is_uptodate check

[Christian Brauner]

On Thu, 10 Apr 2025 15:12:36 +0800, Gou Hao wrote:
> In iomap_adjust_read_range, i is either the first !uptodate block, or it
> is past last for the second loop looking for trailing uptodate blocks.
> Assuming there's no overflow (there's no combination of huge folios and
> tiny blksize) then yeah, there is no point in retesting that the same
> block pointed to by i is uptodate since we hold the folio lock so nobody
> else could have set it uptodate.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] iomap: skip unnecessary ifs_block_is_uptodate check
      https://git.kernel.org/vfs/vfs/c/8e3c15ee0d29