From: Wu Fengguang <fengguang.wu@intel.com>
To: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Jan Kara <jack@suse.cz>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] Fix mapping->writeback_index to point to the last written page
Date: Fri, 4 Mar 2011 10:20:03 +0800 [thread overview]
Message-ID: <20110304022003.GA9213@localhost> (raw)
In-Reply-To: <4D70443A.1010602@ce.jp.nec.com>
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
prev parent reply other threads:[~2011-03-04 2:20 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-25 7:55 [PATCH] Fix mapping->writeback_index to point to the last written page Jun'ichi Nomura
2011-03-02 22:18 ` Jan Kara
2011-03-03 2:26 ` Jun'ichi Nomura
2011-03-03 13:31 ` Wu Fengguang
2011-03-03 14:08 ` Jan Kara
2011-03-04 1:45 ` Jun'ichi Nomura
2011-03-04 2:20 ` Wu Fengguang [this message]
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