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From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Ming Lei <ming.lei@redhat.com>
Cc: Andrea Vai <andrea.vai@unipv.it>,
	"Schmid, Carsten" <Carsten_Schmid@mentor.com>,
	Finn Thain <fthain@telegraphics.com.au>,
	Damien Le Moal <Damien.LeMoal@wdc.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Jens Axboe <axboe@kernel.dk>,
	Johannes Thumshirn <jthumshirn@suse.de>,
	USB list <linux-usb@vger.kernel.org>,
	SCSI development list <linux-scsi@vger.kernel.org>,
	Himanshu Madhani <himanshu.madhani@cavium.com>,
	Hannes Reinecke <hare@suse.com>, Omar Sandoval <osandov@fb.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Hans Holmberg <Hans.Holmberg@wdc.com>,
	Kernel development list <linux-kernel@vger.kernel.org>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: AW: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6
Date: Tue, 10 Dec 2019 21:41:37 -0500
Message-ID: <20191211024137.GB61323@mit.edu> (raw)
In-Reply-To: <20191210080550.GA5699@ming.t460p>

On Tue, Dec 10, 2019 at 04:05:50PM +0800, Ming Lei wrote:
> > > The path[2] is expected behaviour. Not sure path [1] is correct,
> > > given
> > > ext4_release_file() is supposed to be called when this inode is
> > > released. That means the file is closed 4358 times during 1GB file
> > > copying to usb storage.
> > > 
> > > [1] insert requests when returning to user mode from syscall
> > > 
> > >   b'blk_mq_sched_request_inserted'
> > >   b'blk_mq_sched_request_inserted'
> > >   b'dd_insert_requests'
> > >   b'blk_mq_sched_insert_requests'
> > >   b'blk_mq_flush_plug_list'
> > >   b'blk_flush_plug_list'
> > >   b'io_schedule_prepare'
> > >   b'io_schedule'
> > >   b'rq_qos_wait'
> > >   b'wbt_wait'
> > >   b'__rq_qos_throttle'
> > >   b'blk_mq_make_request'
> > >   b'generic_make_request'
> > >   b'submit_bio'
> > >   b'ext4_io_submit'
> > >   b'ext4_writepages'
> > >   b'do_writepages'
> > >   b'__filemap_fdatawrite_range'
> > >   b'ext4_release_file'
> > >   b'__fput'
> > >   b'task_work_run'
> > >   b'exit_to_usermode_loop'
> > >   b'do_syscall_64'
> > >   b'entry_SYSCALL_64_after_hwframe'
> > >     4358

I'm guessing that your workload is repeatedly truncating a file (or
calling open with O_TRUNC) and then writing data to it.  When you do
this, then when the file is closed, we assume that since you were
replacing the previous contents of a file with new contents, that you
would be unhappy if the file contents was replaced by a zero length
file after a crash.  That's because ten years, ago there were a *huge*
number of crappy applications that would replace a file by reading it
into memory, truncating it, and then write out the new contents of the
file.  This could be a high score file for a game, or a KDE or GNOME
state file, etc.

So if someone does open, truncate, write, close, we still immediately
writing out the data on the close, assuming that the programmer really
wanted open, truncate, write, fsync, close, but was too careless to
actually do the right thing.

Some workaround[1] like this is done by all of the major file systems,
and was fallout the agreement from the "O_PONIES"[2] controversy.
This was discussed and agreed to at the 2009 LSF/MM workshop.  (See
the "rename, fsync, and ponies" section.)

[1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/317781/comments/45
[2] https://blahg.josefsipek.net/?p=364
[3] https://lwn.net/Articles/327601/

So if you're seeing a call to filemap_fdatawrite_range as the result
of a fput, that's why.

In any case, this behavior has been around for a decade, and it
appears to be incidental to your performance difficulties with your
USB thumbdrive and block-mq.

						- Ted

  reply index

Thread overview: 102+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <307581a490b610c3025ee80f79a465a89d68ed19.camel@unipv.it>
2019-08-20 17:13 ` Alan Stern
2019-08-23 10:39   ` Andrea Vai
2019-08-23 20:42     ` Alan Stern
2019-08-26  6:09       ` Andrea Vai
2019-08-26 16:33         ` Alan Stern
2019-09-18 15:25           ` Andrea Vai
2019-09-18 16:30             ` Alan Stern
2019-09-19  7:33               ` Andrea Vai
2019-09-19 17:54                 ` Alan Stern
2019-09-20  7:25                   ` Andrea Vai
2019-09-20  7:44                     ` Greg KH
2019-09-19  8:26               ` Damien Le Moal
2019-09-19  8:55                 ` Ming Lei
2019-09-19  9:09                   ` Damien Le Moal
2019-09-19  9:21                     ` Ming Lei
2019-09-19 14:01                 ` Alan Stern
2019-09-19 14:14                   ` Damien Le Moal
2019-09-20  7:03                     ` Andrea Vai
2019-09-25 19:30                       ` Alan Stern
2019-09-25 19:36                         ` Jens Axboe
2019-09-27 15:47                           ` Andrea Vai
2019-11-04 16:00                             ` Andrea Vai
2019-11-04 18:20                               ` Alan Stern
2019-11-05 11:48                                 ` Andrea Vai
2019-11-05 18:31                                   ` Alan Stern
2019-11-05 23:29                                     ` Jens Axboe
2019-11-06 16:03                                       ` Alan Stern
2019-11-06 22:13                                         ` Damien Le Moal
2019-11-07  7:04                                           ` Andrea Vai
2019-11-07  7:54                                             ` Damien Le Moal
2019-11-07 18:59                                               ` Andrea Vai
2019-11-08  8:42                                                 ` Damien Le Moal
2019-11-08 14:33                                                   ` Jens Axboe
2019-11-11 10:46                                                     ` Andrea Vai
2019-11-09 10:09                                                   ` Ming Lei
2019-11-09 22:28                                                 ` Ming Lei
2019-11-11 10:50                                                   ` Andrea Vai
2019-11-11 11:05                                                     ` Ming Lei
2019-11-11 11:13                                                       ` Andrea Vai
2019-11-22 19:16                                                   ` Andrea Vai
2019-11-23  7:28                                                     ` Ming Lei
2019-11-23 15:44                                                       ` Andrea Vai
2019-11-25  3:54                                                         ` Ming Lei
2019-11-25 10:11                                                           ` Andrea Vai
2019-11-25 10:29                                                             ` Ming Lei
2019-11-25 14:58                                                               ` Andrea Vai
2019-11-25 15:15                                                                 ` Ming Lei
2019-11-25 18:51                                                                   ` Andrea Vai
2019-11-26  2:32                                                                     ` Ming Lei
2019-11-26  7:46                                                                       ` Andrea Vai
2019-11-26  9:15                                                                         ` Ming Lei
2019-11-26 10:24                                                                           ` Ming Lei
2019-11-26 11:14                                                                           ` Andrea Vai
2019-11-27  2:05                                                                             ` Ming Lei
2019-11-27  9:39                                                                               ` Andrea Vai
2019-11-27 13:08                                                                                 ` Ming Lei
2019-11-27 15:01                                                                                   ` Andrea Vai
2019-11-27  0:21                                                                         ` Finn Thain
2019-11-27  8:14                                                                           ` AW: " Schmid, Carsten
2019-11-27 21:49                                                                             ` Finn Thain
2019-11-28  7:46                                                                             ` Andrea Vai
2019-11-28  8:12                                                                               ` AW: " Schmid, Carsten
2019-11-28 11:40                                                                                 ` Andrea Vai
2019-11-28 17:39                                                                                 ` Alan Stern
2019-11-28  9:17                                                                               ` Ming Lei
2019-11-28 17:34                                                                                 ` Andrea Vai
2019-11-29  0:57                                                                                   ` Ming Lei
2019-11-29  2:35                                                                                     ` Ming Lei
2019-11-29 14:41                                                                                       ` Andrea Vai
2019-12-03  2:23                                                                                         ` Ming Lei
2019-12-10  7:35                                                                                           ` Andrea Vai
2019-12-10  8:05                                                                                             ` Ming Lei
2019-12-11  2:41                                                                                               ` Theodore Y. Ts'o [this message]
2019-12-11  4:00                                                                                                 ` Ming Lei
2019-12-11 16:07                                                                                                   ` Theodore Y. Ts'o
2019-12-11 21:33                                                                                                     ` Ming Lei
2019-12-12  7:34                                                                                                       ` Andrea Vai
2019-12-18  8:25                                                                                                       ` Andrea Vai
2019-12-18  9:48                                                                                                         ` Ming Lei
     [not found]                                                                                                           ` <b1b6a0e9d690ecd9432025acd2db4ac09f834040.camel@unipv.it>
2019-12-23 13:08                                                                                                             ` Ming Lei
2019-12-23 14:02                                                                                                               ` Andrea Vai
2019-12-24  1:32                                                                                                                 ` Ming Lei
2019-12-24  8:04                                                                                                                   ` Andrea Vai
2019-12-24  8:47                                                                                                                     ` Ming Lei
2019-12-23 16:26                                                                                                               ` Theodore Y. Ts'o
2019-12-23 16:29                                                                                                                 ` Andrea Vai
2019-12-23 17:22                                                                                                                   ` Theodore Y. Ts'o
2019-12-23 18:45                                                                                                                     ` Andrea Vai
2019-12-23 19:53                                                                                                                       ` Theodore Y. Ts'o
2019-12-24  1:27                                                                                                                         ` Ming Lei
2019-12-24  6:49                                                                                                                           ` Andrea Vai
2019-12-24  8:51                                                                                                                           ` Andrea Vai
2019-12-24  9:35                                                                                                                             ` Ming Lei
2019-12-25  5:17                                                                                                                           ` Theodore Y. Ts'o
2019-12-26  2:27                                                                                                                             ` Ming Lei
2019-12-26  3:30                                                                                                                               ` Theodore Y. Ts'o
2019-12-26  8:37                                                                                                                                 ` Ming Lei
2020-01-07  7:51                                                                                                                                   ` Andrea Vai
     [not found]                                                                                                                                 ` <20200101074310.10904-1-hdanton@sina.com>
2020-01-01 13:53                                                                                                                                   ` slow IO on USB media Ming Lei
2019-11-29 11:44                                                                                     ` AW: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6 Bernd Schubert
2019-12-02  7:01                                                                                       ` Andrea Vai
2019-11-28 17:10                                                                           ` Andrea Vai

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