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From: Mike Snitzer <snitzer@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Spelic <spelic@shiftmail.org>,
	device-mapper development <dm-devel@redhat.com>,
	linux-ext4@vger.kernel.org, xfs@oss.sgi.com
Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard
Date: Mon, 18 Jun 2012 23:12:42 -0400	[thread overview]
Message-ID: <20120619031241.GA3884@redhat.com> (raw)
In-Reply-To: <20120619015745.GJ25389@dastard>

On Mon, Jun 18 2012 at  9:57pm -0400,
Dave Chinner <david@fromorbit.com> wrote:

> On Mon, Jun 18, 2012 at 11:33:50PM +0200, Spelic wrote:
>
> > Please note that since I am above MD raid5 (I believe this is the
> > reason), the passdown of discards does not work, as my dmesg says:
> > [160508.497879] device-mapper: thin: Discard unsupported by data
> > device (dm-1): Disabling discard passdown.
> > but AFAIU, unless there is a thinp bug, this should not affect the
> > unmapping of thin blocks by fstrimming xfs... and in fact ext4 is
> > able to do that.
> 
> Does ext4 report that same error?

That message says the underlying device doesn't support discards
(because it is an MD device).  But the thinp device still has discards
enabled -- it just won't pass the discards down to the underlying data
device.

So yes, it'll happen with ext4 -- it is generated when the thin-pool
device is loaded (which happens independent of the filesystem that is
layered ontop).

The discards still inform the thin-pool that the corresponding extents
are no longer allocated.

WARNING: multiple messages have this Message-ID (diff)
From: Mike Snitzer <snitzer@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: device-mapper development <dm-devel@redhat.com>,
	linux-ext4@vger.kernel.org, xfs@oss.sgi.com,
	Spelic <spelic@shiftmail.org>
Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard
Date: Mon, 18 Jun 2012 23:12:42 -0400	[thread overview]
Message-ID: <20120619031241.GA3884@redhat.com> (raw)
In-Reply-To: <20120619015745.GJ25389@dastard>

On Mon, Jun 18 2012 at  9:57pm -0400,
Dave Chinner <david@fromorbit.com> wrote:

> On Mon, Jun 18, 2012 at 11:33:50PM +0200, Spelic wrote:
>
> > Please note that since I am above MD raid5 (I believe this is the
> > reason), the passdown of discards does not work, as my dmesg says:
> > [160508.497879] device-mapper: thin: Discard unsupported by data
> > device (dm-1): Disabling discard passdown.
> > but AFAIU, unless there is a thinp bug, this should not affect the
> > unmapping of thin blocks by fstrimming xfs... and in fact ext4 is
> > able to do that.
> 
> Does ext4 report that same error?

That message says the underlying device doesn't support discards
(because it is an MD device).  But the thinp device still has discards
enabled -- it just won't pass the discards down to the underlying data
device.

So yes, it'll happen with ext4 -- it is generated when the thin-pool
device is loaded (which happens independent of the filesystem that is
layered ontop).

The discards still inform the thin-pool that the corresponding extents
are no longer allocated.

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  reply	other threads:[~2012-06-19  3:12 UTC|newest]

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-06-18 21:33 Ext4 and xfs problems in dm-thin on allocation and discard Spelic
2012-06-18 21:33 ` Spelic
2012-06-19  1:57 ` Dave Chinner
2012-06-19  1:57   ` Dave Chinner
2012-06-19  3:12   ` Mike Snitzer [this message]
2012-06-19  3:12     ` Mike Snitzer
2012-06-19  6:32     ` Lukáš Czerner
2012-06-19  6:32       ` Lukáš Czerner
2012-06-19 11:29       ` Spelic
2012-06-19 11:29         ` Spelic
2012-06-19 12:20         ` Lukáš Czerner
2012-06-19 12:20           ` Lukáš Czerner
2012-06-19 13:34         ` Mike Snitzer
2012-06-19 13:34           ` Mike Snitzer
2012-06-19 13:16       ` Mike Snitzer
2012-06-19 13:16         ` Mike Snitzer
2012-06-19 13:25         ` Lukáš Czerner
2012-06-19 13:25           ` Lukáš Czerner
2012-06-19 13:30           ` Mike Snitzer
2012-06-19 13:30             ` Mike Snitzer
2012-06-19 13:52             ` Spelic
2012-06-19 13:52               ` Spelic
2012-06-19 14:05               ` Eric Sandeen
2012-06-19 14:05                 ` Eric Sandeen
2012-06-19 14:44               ` Mike Snitzer
2012-06-19 14:44                 ` Mike Snitzer
2012-06-19 18:48                 ` Mike Snitzer
2012-06-19 18:48                   ` Mike Snitzer
2012-06-19 20:06                   ` Dave Chinner
2012-06-19 20:06                     ` Dave Chinner
2012-06-19 20:21                     ` Ted Ts'o
2012-06-19 20:21                       ` Ted Ts'o
2012-06-19 20:39                       ` Dave Chinner
2012-06-19 20:39                         ` Dave Chinner
2012-06-20  9:01                         ` Christoph Hellwig
2012-06-20  9:01                           ` Christoph Hellwig
2012-06-19 21:37                     ` Spelic
2012-06-19 21:37                       ` Spelic
2012-06-19 23:12                       ` Dave Chinner
2012-06-19 23:12                         ` Dave Chinner
2012-06-20 12:11   ` Spelic
2012-06-20 12:11     ` Spelic
2012-06-20 22:53     ` Dave Chinner
2012-06-20 22:53       ` Dave Chinner
2012-06-21 17:47       ` Mike Snitzer
2012-06-21 17:47         ` Mike Snitzer
2012-06-21 23:29         ` Dave Chinner
2012-06-21 23:29           ` Dave Chinner
2012-07-01 14:53         ` Paolo Bonzini
2012-07-01 14:53           ` Paolo Bonzini
2012-07-02 13:00           ` Mike Snitzer
2012-07-02 13:00             ` Mike Snitzer
2012-07-02 13:15             ` Paolo Bonzini
2012-07-02 13:15               ` Paolo Bonzini
2012-06-19 14:09 ` Lukáš Czerner
2012-06-19 14:09   ` Lukáš Czerner
2012-06-19 14:19   ` Ted Ts'o
2012-06-19 14:19     ` Ted Ts'o
2012-06-19 14:23     ` Eric Sandeen
2012-06-19 14:23       ` Eric Sandeen
2012-06-19 14:37     ` Lukáš Czerner
2012-06-19 14:37       ` Lukáš Czerner
2012-06-19 14:43     ` [dm-devel] " Alasdair G Kergon
2012-06-19 14:43       ` Alasdair G Kergon
2012-06-19 15:28       ` Mike Snitzer
2012-06-19 15:28         ` Mike Snitzer
2012-06-19 16:03         ` [dm-devel] " Alasdair G Kergon
2012-06-19 16:03           ` Alasdair G Kergon
2012-06-19 19:58         ` Ted Ts'o
2012-06-19 19:58           ` Ted Ts'o
2012-06-19 20:44           ` Mike Snitzer
2012-06-19 20:44             ` Mike Snitzer

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