From: Chris Mason <chris.mason@oracle.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] block: fix DISCARD_BARRIER requests
Date: Thu, 17 Jun 2010 15:22:17 -0400 [thread overview]
Message-ID: <20100617192217.GT27466@think> (raw)
In-Reply-To: <20100617165453.GA15824@lst.de>
On Thu, Jun 17, 2010 at 06:54:53PM +0200, Christoph Hellwig wrote:
> On Thu, Jun 17, 2010 at 10:10:18AM +0200, Jens Axboe wrote:
> > Thanks, applied. There was a recent problem report on btrfs using
> > discard, could possibly explain it if Chris assumed it was a full
> > barrier.
>
> We actually have a much bigger issue with the DISCARD_BARRIER type.
> If the discard request needs to get split into multiple smaller ones
> we don't keep the queue drained atomically around them, so requests
> could sneak inbetween them. Depending on how the realtime discard
> is implemented that could cause issues. In my XFS prototype for it
> I only deleted the extents from the tracking betree after the discard
> request has returned, but other filesystems rely on full barrier
> semantics of DISCARD_BARRIER this could cause real problems.
btrfs needs to know that a write after the discard returns won't cross
the discard, but beyond that we're happy with anything.
-chris
next prev parent reply other threads:[~2010-06-17 19:23 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-17 7:54 [PATCH] block: fix DISCARD_BARRIER requests Christoph Hellwig
2010-06-17 8:10 ` Jens Axboe
2010-06-17 11:49 ` Matthew Wilcox
2010-06-17 12:06 ` Jens Axboe
2010-06-17 16:54 ` Christoph Hellwig
2010-06-17 19:22 ` Chris Mason [this message]
2010-06-18 13:29 ` Kyungmin Park
2010-06-19 2:22 ` Kyungmin Park
2010-06-18 15:29 ` Jamie Lokier
2010-06-18 20:30 ` Chris Mason
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