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@xxxxxxxxxx>
> > Signed-off-by: Wang Jianchao <wangjc136@xxxxxxxxx>

...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@xxxxxxxxxx>

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))) {