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Date:	Tue, 19 Jun 2012 09:34:42 -0400
From:	Mike Snitzer <>
To:	Spelic <>
Cc:	Lukáš Czerner <>,
	Dave Chinner <>,,
	device-mapper development <>,
Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard

On Tue, Jun 19 2012 at  7:29am -0400,
Spelic <> wrote:

> On 06/19/12 08:32, Lukáš Czerner wrote:
> >
> >So do I understand correctly that even though the discard came
> >through and thinp took advantage of it it still returns EOPNOTSUPP ?
> >This seems rather suboptimal. IIRC there was a discussion to add an
> >option to enable/disable sending discard in thinp target down
> >to the device.
> I'll ask this too...
> do I understand correctly that dm-thin returns EOPNOTSUPP to the
> filesystem layer even though it is using the discard to unmap
> blocks, and at that point XFS stops sending discards down there
> (while ext4 keeps sending them)?

Are you actually seeing that?  Or are you just seizing on Lukas'

> This looks like a bug of dm-thin to me. Discards are "supported" in
> such a scenario.
> Do you have a patch for dm-thin so to prevent it sending EOPTNOTSUPP ?

thinp should _not_ be sending -EOPNOTSUPP unless 'ignore_discard' is
provided as a feature when loading thin-pool's DM  table.
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