On Fri, Mar 04, 2011 at 09:45:30AM +0800, Jun'ichi Nomura wrote: > On 03/03/11 23:08, Jan Kara wrote: > > On Thu 03-03-11 21:31:19, Wu Fengguang wrote: > >> On Thu, Mar 03, 2011 at 10:26:19AM +0800, Jun'ichi Nomura wrote: >> [2nd writeback session after 35sec] >> flush-8:0-2743 4606: block_bio_queue: 8,0 W 94898562 + 8 >> flush-8:0-2743 4606: block_bio_queue: 8,0 W 94898570 + 8 >> flush-8:0-2743 4606: block_bio_queue: 8,0 W 94898578 + 8 >> ... >> kworker/0:1-11 4606: block_rq_issue: 8,0 W 0 () 94898562 + 640 >> kworker/0:1-11 4606: block_rq_issue: 8,0 W 0 () 94899202 + 72 >> ... > >> > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899962 + 8 > >> > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899970 + 8 > >> > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899978 + 8 > >> > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899986 + 8 > >> > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899994 + 8 > >> ==> > kworker/0:1-11 4606: block_rq_issue: 8,0 W 0 () 94899962 + 40 > >> > >> flush-8:0-2743 4606: block_bio_queue: 8,0 W 94898554 + 8 > >> ==> > >> flush-8:0-2743 4606: block_rq_issue: 8,0 W 0 () 94898554 + 8 > >> > >> I'd expect the wrapped around 94898554+8 to be merged with 94899962+8. > > How could they be merged? They are not continguous... Oops, it is. It's 94898562+8 that is continuous with 94898554+8, however the former has been submitted on max_sectors limit. So 94898554+8 lost the chance to get merged. > >> Why kworker/0:1-11 is submitting the request early? And the second > >> request is submitted by flush-8:0-2743. > > I'm not sure about that either - but I think that kworker is submitting > > the work when unplug happens while flush ends up doing it when the queue is > > alredy unplugged. > > Yes. For the above case, it was unplug. > > For other cases, the reason was max_sectors. > Before writeback wraps around, the request has already grown to > max_sectors size (~512KB) and doesn't accept new merge. Yup, good explanation! Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
