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Date: Wed, 9 Nov 2011 07:12:49 -0500
From: Chris Mason <chris.mason@oracle.com>
To: Jan Schmidt <list.btrfs@jan-o-sch.net>
Cc: linux-btrfs <linux-btrfs@vger.kernel.org>,
        Christoph Hellwig <hch@infradead.org>, Arne Jansen <sensille@gmx.net>,
        Andrea Gelmini <andrea.gelmini@gmail.com>,
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Subject: Re: [GIT PULL] Btrfs pull request
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On Wed, Nov 09, 2011 at 11:29:31AM +0100, Jan Schmidt wrote:
> Am 09.11.2011 08:48, schrieb Christoph Hellwig:
> >On Tue, Nov 08, 2011 at 08:07:01PM -0500, Chris Mason wrote:
> >>Looks like bio_add_page() is failing and we're getting the enomem from
> >>there.  LVM is only letting us put one page in each bio.
> >
> >Yes, at the moment all bio based DM targets only allow single page I/O.
> 
> Wait. If I got that correctly, each bio_add_page needs special
> ENOMEM treatment (assuming the target could always be a device
> mapper target), right?
> 
> "grep bio_add_page fs/btrfs/*.c" will make you unhappy.

You can always add a single page into a bio.  We do need to deal better
with mixed devices where some have a low limit and some a high limit.

-chris