[PATCH V2] xfs: use roundup_pow_of_two instead of ffs during xlog_find_tail

[PATCH V2] xfs: use roundup_pow_of_two instead of ffs during xlog_find_tail

[Wang Jianchao]

In our production environment, we find that mounting a 500M /boot
which is umount cleanly needs ~6s. One cause is that ffs() is
used by xlog_write_log_records() to decide the buffer size. It
can cause a lot of small IO easily when xlog_clear_stale_blocks()
needs to wrap around the end of log area and log head block is
not power of two. Things are similar in xlog_find_verify_cycle().

The code is able to handed bigger buffer very well, we can use
roundup_pow_of_two() to replace ffs() directly to avoid small
and sychronous IOs.

Changes in V1:
 - Also replace the ffs in xlog_find_verify_cycle()

Signed-off-by: Wang Jianchao <wangjc136@midea.com>
---

 fs/xfs/xfs_log_recover.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 82c81d20459d..13b94d2e605b 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -329,7 +329,7 @@ xlog_find_verify_cycle(
 	 * try a smaller size.  We need to be able to read at least
 	 * a log sector, or we're out of luck.
 	 */
-	bufblks = 1 << ffs(nbblks);
+	bufblks = roundup_pow_of_two(nbblks);
 	while (bufblks > log->l_logBBsize)
 		bufblks >>= 1;
 	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {
@@ -1528,7 +1528,7 @@ xlog_write_log_records(
 	 * a smaller size.  We need to be able to write at least a
 	 * log sector, or we're out of luck.
 	 */
-	bufblks = 1 << ffs(blocks);
+	bufblks = roundup_pow_of_two(blocks);
 	while (bufblks > log->l_logBBsize)
 		bufblks >>= 1;
 	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {
-- 
2.34.1

Re: [PATCH V2] xfs: use roundup_pow_of_two instead of ffs during xlog_find_tail

[Dave Chinner]

On Tue, Sep 12, 2023 at 03:20:56PM +0800, Wang Jianchao wrote:
> 
> In our production environment, we find that mounting a 500M /boot
> which is umount cleanly needs ~6s. One cause is that ffs() is
> used by xlog_write_log_records() to decide the buffer size. It
> can cause a lot of small IO easily when xlog_clear_stale_blocks()
> needs to wrap around the end of log area and log head block is
> not power of two. Things are similar in xlog_find_verify_cycle().
> 
> The code is able to handed bigger buffer very well, we can use
> roundup_pow_of_two() to replace ffs() directly to avoid small
> and sychronous IOs.
> 
> Changes in V1:
>  - Also replace the ffs in xlog_find_verify_cycle()

Change logs go either below the --- line or in the cover letter,
not the commit itself.

Other than that, the change looks ok. The use of ffs() was added in
2002 simply to make buffers a power-of-2 size. I don't think it had
anything to do with trying to maximise the actual buffer size at
all, otherwise it would have made to use fls() like
roundup_pow_of_two() does...

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com

Re: [PATCH V2] xfs: use roundup_pow_of_two instead of ffs during xlog_find_tail

[Wang Jianchao]

On 2023/9/13 06:44, Dave Chinner wrote:
> On Tue, Sep 12, 2023 at 03:20:56PM +0800, Wang Jianchao wrote:
>>
>> In our production environment, we find that mounting a 500M /boot
>> which is umount cleanly needs ~6s. One cause is that ffs() is
>> used by xlog_write_log_records() to decide the buffer size. It
>> can cause a lot of small IO easily when xlog_clear_stale_blocks()
>> needs to wrap around the end of log area and log head block is
>> not power of two. Things are similar in xlog_find_verify_cycle().
>>
>> The code is able to handed bigger buffer very well, we can use
>> roundup_pow_of_two() to replace ffs() directly to avoid small
>> and sychronous IOs.
>>
>> Changes in V1:
>>  - Also replace the ffs in xlog_find_verify_cycle()
> 
> Change logs go either below the --- line or in the cover letter,
> not the commit itself.

OK

> 
> Other than that, the change looks ok. The use of ffs() was added in
> 2002 simply to make buffers a power-of-2 size. I don't think it had
> anything to do with trying to maximise the actual buffer size at
> all, otherwise it would have made to use fls() like
> roundup_pow_of_two() does...
> 
> Reviewed-by: Dave Chinner <dchinner@redhat.com>
> 

Thanks
Jianchao

[PATCH V3] xfs: use roundup_pow_of_two instead of ffs during xlog_find_tail

[Wang Jianchao]

In our production environment, we find that mounting a 500M /boot
which is umount cleanly needs ~6s. One cause is that ffs() is
used by xlog_write_log_records() to decide the buffer size. It
can cause a lot of small IO easily when xlog_clear_stale_blocks()
needs to wrap around the end of log area and log head block is
not power of two. Things are similar in xlog_find_verify_cycle().

The code is able to handed bigger buffer very well, we can use
roundup_pow_of_two() to replace ffs() directly to avoid small
and sychronous IOs.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Wang Jianchao <wangjc136@midea.com>
---

Changes in V2:
 - Move change log below "---"
 - Add reviewed-by Dave Chinner tag

Changes in V1:
 - Also replace the ffs in xlog_find_verify_cycle()

 fs/xfs/xfs_log_recover.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 82c81d20459d..13b94d2e605b 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -329,7 +329,7 @@ xlog_find_verify_cycle(
 	 * try a smaller size.  We need to be able to read at least
 	 * a log sector, or we're out of luck.
 	 */
-	bufblks = 1 << ffs(nbblks);
+	bufblks = roundup_pow_of_two(nbblks);
 	while (bufblks > log->l_logBBsize)
 		bufblks >>= 1;
 	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {
@@ -1528,7 +1528,7 @@ xlog_write_log_records(
 	 * a smaller size.  We need to be able to write at least a
 	 * log sector, or we're out of luck.
 	 */
-	bufblks = 1 << ffs(blocks);
+	bufblks = roundup_pow_of_two(blocks);
 	while (bufblks > log->l_logBBsize)
 		bufblks >>= 1;
 	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {
-- 
2.34.1

Re: [PATCH V3] xfs: use roundup_pow_of_two instead of ffs during xlog_find_tail

[Wang Jianchao]

Ping ? Do I need other update on this patch ?

Thanks
Jianchao

On 2023/9/13 09:38, Wang Jianchao wrote:
> 
> In our production environment, we find that mounting a 500M /boot
> which is umount cleanly needs ~6s. One cause is that ffs() is
> used by xlog_write_log_records() to decide the buffer size. It
> can cause a lot of small IO easily when xlog_clear_stale_blocks()
> needs to wrap around the end of log area and log head block is
> not power of two. Things are similar in xlog_find_verify_cycle().
> 
> The code is able to handed bigger buffer very well, we can use
> roundup_pow_of_two() to replace ffs() directly to avoid small
> and sychronous IOs.
> 
> Reviewed-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Wang Jianchao <wangjc136@midea.com>
> ---
> 
> Changes in V2:
>  - Move change log below "---"
>  - Add reviewed-by Dave Chinner tag
> 
> Changes in V1:
>  - Also replace the ffs in xlog_find_verify_cycle()
> 
>  fs/xfs/xfs_log_recover.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index 82c81d20459d..13b94d2e605b 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -329,7 +329,7 @@ xlog_find_verify_cycle(
>  	 * try a smaller size.  We need to be able to read at least
>  	 * a log sector, or we're out of luck.
>  	 */
> -	bufblks = 1 << ffs(nbblks);
> +	bufblks = roundup_pow_of_two(nbblks);
>  	while (bufblks > log->l_logBBsize)
>  		bufblks >>= 1;
>  	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {
> @@ -1528,7 +1528,7 @@ xlog_write_log_records(
>  	 * a smaller size.  We need to be able to write at least a
>  	 * log sector, or we're out of luck.
>  	 */
> -	bufblks = 1 << ffs(blocks);
> +	bufblks = roundup_pow_of_two(blocks);
>  	while (bufblks > log->l_logBBsize)
>  		bufblks >>= 1;
>  	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {

Re: [PATCH V3] xfs: use roundup_pow_of_two instead of ffs during xlog_find_tail

[Darrick J. Wong]

On Tue, Sep 19, 2023 at 10:06:56AM +0800, Wang Jianchao wrote:
> Ping ? Do I need other update on this patch ?

Nope, I think this is ok...

> Thanks
> Jianchao
> 
> On 2023/9/13 09:38, Wang Jianchao wrote:
> > 
> > In our production environment, we find that mounting a 500M /boot
> > which is umount cleanly needs ~6s. One cause is that ffs() is
> > used by xlog_write_log_records() to decide the buffer size. It
> > can cause a lot of small IO easily when xlog_clear_stale_blocks()
> > needs to wrap around the end of log area and log head block is
> > not power of two. Things are similar in xlog_find_verify_cycle().
> > 
> > The code is able to handed bigger buffer very well, we can use
> > roundup_pow_of_two() to replace ffs() directly to avoid small
> > and sychronous IOs.
> > 
> > Reviewed-by: Dave Chinner <dchinner@redhat.com>
> > Signed-off-by: Wang Jianchao <wangjc136@midea.com>

...so let's see if the release manager will take this patch.

Chandan?  Could you pull in the various one-off patches floating around
on the list that have passed review?  ;)

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

PS: If you'd like to send a pull request to push things along, please do

--D

> > ---
> > 
> > Changes in V2:
> >  - Move change log below "---"
> >  - Add reviewed-by Dave Chinner tag
> > 
> > Changes in V1:
> >  - Also replace the ffs in xlog_find_verify_cycle()
> > 
> >  fs/xfs/xfs_log_recover.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> > index 82c81d20459d..13b94d2e605b 100644
> > --- a/fs/xfs/xfs_log_recover.c
> > +++ b/fs/xfs/xfs_log_recover.c
> > @@ -329,7 +329,7 @@ xlog_find_verify_cycle(
> >  	 * try a smaller size.  We need to be able to read at least
> >  	 * a log sector, or we're out of luck.
> >  	 */
> > -	bufblks = 1 << ffs(nbblks);
> > +	bufblks = roundup_pow_of_two(nbblks);
> >  	while (bufblks > log->l_logBBsize)
> >  		bufblks >>= 1;
> >  	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {
> > @@ -1528,7 +1528,7 @@ xlog_write_log_records(
> >  	 * a smaller size.  We need to be able to write at least a
> >  	 * log sector, or we're out of luck.
> >  	 */
> > -	bufblks = 1 << ffs(blocks);
> > +	bufblks = roundup_pow_of_two(blocks);
> >  	while (bufblks > log->l_logBBsize)
> >  		bufblks >>= 1;
> >  	while (!(buffer = xlog_alloc_buffer(log, bufblks))) {

Re: [PATCH V3] xfs: use roundup_pow_of_two instead of ffs during xlog_find_tail

[Chandan Babu R]

On Mon, Sep 18, 2023 at 08:21:38 PM -0700, Darrick J. Wong wrote:
> On Tue, Sep 19, 2023 at 10:06:56AM +0800, Wang Jianchao wrote:
>> Ping ? Do I need other update on this patch ?
>
> Nope, I think this is ok...
>
>> Thanks
>> Jianchao
>> 
>> On 2023/9/13 09:38, Wang Jianchao wrote:
>> > 
>> > In our production environment, we find that mounting a 500M /boot
>> > which is umount cleanly needs ~6s. One cause is that ffs() is
>> > used by xlog_write_log_records() to decide the buffer size. It
>> > can cause a lot of small IO easily when xlog_clear_stale_blocks()
>> > needs to wrap around the end of log area and log head block is
>> > not power of two. Things are similar in xlog_find_verify_cycle().
>> > 
>> > The code is able to handed bigger buffer very well, we can use
>> > roundup_pow_of_two() to replace ffs() directly to avoid small
>> > and sychronous IOs.
>> > 
>> > Reviewed-by: Dave Chinner <dchinner@redhat.com>
>> > Signed-off-by: Wang Jianchao <wangjc136@midea.com>
>
> ...so let's see if the release manager will take this patch.
>
> Chandan?  Could you pull in the various one-off patches floating around
> on the list that have passed review?  ;)

I had picked this patch along with others sometime last week.

I have pushed the new set of commits to official xfs-linux git repository and
sent the announcement mail around 30 mins ago.

>
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
>
> PS: If you'd like to send a pull request to push things along, please do
>

-- 
Chandan