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@xxxxxxxxxx> -- Dave Chinner david@xxxxxxxxxxxxx
