linux-kernel - Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY

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Date:	Mon, 24 Aug 2015 18:55:49 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Eryu Guan <eguan@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
	linux-kernel@...r.kernel.org, xfs@....sgi.com, axboe@...com,
	linux-fsdevel@...r.kernel.org, Jan Kara <jack@...e.com>,
	Tejun Heo <tj@...nel.org>, kernel-team@...com
Subject: Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME
 inodes

On Mon, Aug 24, 2015 at 04:34:37PM +0800, Eryu Guan wrote:
> On Mon, Aug 24, 2015 at 04:24:25PM +1000, Dave Chinner wrote:
> > On Mon, Aug 24, 2015 at 11:18:16AM +0800, Eryu Guan wrote:
> > > On Mon, Aug 24, 2015 at 11:11:23AM +1000, Dave Chinner wrote:
> > > > 
> > > > Eryu, can you change the way you run the event trace to be:
> > > > 
> > > > $ sudo trace-cmd <options> -o <outfile location> ./check <test options>
> > > > 
> > > > rather than running the trace as a background operation elsewhere?
> > > > Maybe that will give better results.
> [snip]
> > Anyway, Eryum long and short of it is that you don't need to worry
> > about testing all the different combinations - we now know that the
> > completion events are occurring, so let's focus on whether the sync
> > code is not waiting for them correctly. Can you trace the following
> > events:
> > 
> > 	xfs_log_force
> > 	xfs_setfilesize
> > 	writeback_queue
> > 	writeback_exec
> > 	writeback_start
> > 	writeback_queue_io
> > 	writeback_written
> > 	writeback_pages_written
> > 
> > basically I'm trying to see if we've got all the BDI events as we'd
> > expect then to be queued and run for sync, and when the ->sync_fs
> > call occurs during the sync process before shutdown and unmount...
> 
> I collected two versions of trace info with crc enabled.
> 
> http://128.199.137.77/writeback-crc/
> 
> This version traced the same events as previous runs.
> 
> http://128.199.137.77/writeback-crc-v2/
> 
> And this version only traced the events you listed above.

OK, I'll look into these later.

> And the results of other tests to check(all done with v4 xfs, with no
> tracepoints enabled):
> 
> > Other things to check (separately):
> >	- change godown to godown -f
> 
> Passed 100 loops.

Yup, I expected that from the last set of traces - the "-f" flag
triggers a log force before shutdown, and that flushes out
transactions that sync missed.

> >	- add a "sleep 5" before running godown after sync
> 
> Failed, if you need the trace info please let me know.

Expected, still nothing to flush transactions before shutdown.

> >	- add a "sleep 5; sync" before running godown
> 
> Passed 100 loops.

expected - sync flushed the transactions it missed on the first
pass.

Thanks for running these tests!

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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