| Message ID | CY8PR05MB9378060FDF6C7E15589EB668CDF1A@CY8PR05MB9378.namprd05.prod.outlook.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | [V2] xfs: use roundup_pow_of_two instead of ffs during xlog_find_tail | expand |
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>
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
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))) {
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(-)