linux-ext4 - Re: [dm-devel] do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target]

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Message-ID: <alpine.LFD.2.00.1105041858010.27793@dhcp-27-109.brq.redhat.com>
Date:	Wed, 4 May 2011 19:02:06 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>
cc:	Eric Sandeen <sandeen@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Lukas Czerner <lczerner@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
	DarkNovaNick@...il.com, linux-lvm@...hat.com,
	linux-ext4@...r.kernel.org
Subject: Re: [dm-devel] do not disable ext4 discards on first discard failure?
 [was: Re: dm snapshot: ignore discards issued to the snapshot-origin
 target]

On Wed, 4 May 2011, Ted Ts'o wrote:

> On Fri, Apr 29, 2011 at 09:28:51AM -0500, Eric Sandeen wrote:
> > On 4/29/11 7:29 AM, Christoph Hellwig wrote:
> > > FYI, that disable discard on failure seems to be an ext4 special and no
> > > one else picked up that stupid idea.  If ext4 wants to misbehave for
> > > that just let them..
> > 
> > It was my "stupid idea," and I'm ok with reverting it ;)
> 
> I think I forgot to send the patch out, but it's been reverted in the
> ext4 master branch, commit id: d9f34504e695.  It's more than a revert,
> actually, since I also dropped error checking for FITRIM.  Otherwise
> an attempt to use FITRIM would stop after hitting the first dm region
> that didn't support discards.
> 
> 						- Ted
> 

However I would very much like to change blkdev_issue_discard() not NOT
return EOPNOTSUPP if QUEUE_FLAG_DISCARD is set, this way we can rely on
EOPNOTSUPP saying really that it is NOT supported. Regardless on ext4
change.

I will send a patch for it, if you guy agree. Also consider BLKDISCARD
which is now broken and this change will fix that!

Thanks!
-Lukas
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