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From: NeilBrown <neilb@suse.de>
To: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>,
	"Theodore Ts'o" <tytso@mit.edu>,
	linux-ext4 <linux-ext4@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH 1/2] bdi: Create a flag to indicate that a backing device needs stable page writes
Date: Tue, 30 Oct 2012 15:48:44 +1100	[thread overview]
Message-ID: <20121030154844.1898f068@notabene.brown> (raw)
In-Reply-To: <yq1ehkg8us1.fsf@sermon.lab.mkp.net>

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On Tue, 30 Oct 2012 00:10:22 -0400 "Martin K. Petersen"
<martin.petersen@oracle.com> wrote:

> >>>>> "Darrick" == Darrick J Wong <darrick.wong@oracle.com> writes:
> 
> Darrick> This creates BDI_CAP_STABLE_WRITES, which indicates that a
> Darrick> device requires stable page writes.  It also plumbs in a sysfs
> Darrick> attribute so that admins can check the device status.
> 
> Might be nice to make the sysfs knob tweakable. Also, don't forget to
> add a suitable blurb to Documentation/ABI/.

 It isn't at all clear to me that having the sysfs knob 'tweakable' is a good
 idea.
 From the md/raid5 perspective, I would want to know for certain whether the
 pages in a give bio are guaranteed not to change, or if they might.
 I could set the BDI_CAP_STABLE_WRITES and believe they will never change, or
 test the BDI_CAP_STABLE_WRITES and let that tell me if they might change or
 not.  But if the bit can be changed at any moment, then it can never be
 trusted and so becomes worthless to me.

 At the very least it should only be possible to change it when there is no
 IO in flight.

NeilBrown


> 
> Feel free to add my Acked-by:
> 


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  reply	other threads:[~2012-10-30  4:48 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-10-26 10:19 semi-stable page writes Darrick J. Wong
2012-10-27  1:35 ` [RFC PATCH 1/2] bdi: Create a flag to indicate that a backing device needs stable " Darrick J. Wong
2012-10-29 18:13   ` Jan Kara
2012-10-29 18:30     ` Jan Kara
2012-10-29 23:48       ` NeilBrown
2012-10-30  0:10         ` Jan Kara
2012-10-30  0:34           ` NeilBrown
2012-10-30 13:38             ` Jan Kara
2012-10-30 21:49               ` NeilBrown
2012-10-30  4:10   ` Martin K. Petersen
2012-10-30  4:48     ` NeilBrown [this message]
2012-10-30 12:19       ` Martin K. Petersen
2012-10-30 20:14         ` Darrick J. Wong
2012-10-30 22:14           ` NeilBrown
2012-10-30 23:58             ` Boaz Harrosh
2012-10-31  8:56             ` Darrick J. Wong
2012-10-31 11:56               ` Jan Kara
2012-10-31 19:36                 ` Darrick J. Wong
2012-10-31 23:12                   ` Boaz Harrosh
2012-11-01  5:51                     ` Darrick J. Wong
2012-11-01  6:25                       ` Boaz Harrosh
2012-11-01  8:59                   ` Jan Kara
2012-11-01 17:24                     ` Boaz Harrosh
2012-11-01 22:42                       ` Jan Kara
2012-10-30 22:40   ` Boaz Harrosh
2012-10-27  1:36 ` [RFC PATCH 2/2] mm: Gate stable page writes on the bdi flag Darrick J. Wong
2012-10-29 18:28   ` Jan Kara
2012-10-31  8:58     ` Darrick J. Wong
2012-10-29 22:01 ` semi-stable page writes Dave Chinner
2012-10-30  1:00   ` Theodore Ts'o
2012-10-30 23:30     ` Dave Chinner
2012-10-31 11:45       ` Jan Kara
2012-10-30 20:40   ` Darrick J. Wong
2012-10-30 23:43     ` Dave Chinner
2012-10-31  9:05       ` Darrick J. Wong

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