linux-ext4 - Re: Ext4 and xfs problems in dm-thin on allocation and discard

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Message-id: <4FE062B3.7080702@shiftmail.org>
Date:	Tue, 19 Jun 2012 13:29:55 +0200
From:	Spelic <spelic@...ftmail.org>
To:	Lukáš Czerner <lczerner@...hat.com>
Cc:	Mike Snitzer <snitzer@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	Spelic <spelic@...ftmail.org>,
	device-mapper development <dm-devel@...hat.com>,
	linux-ext4@...r.kernel.org, xfs@....sgi.com
Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard

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)?

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 ?

Thank you
S.
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