From: Matthew Wilcox <mawilcox@microsoft.com>
Subject: RE: [PATCH v2 2/9] ext2: tell DAX the size of allocation holes
Date: Sat, 10 Sep 2016 07:52:53 +0000
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Cc: Ross Zwisler <ross.zwisler@linux.intel.com>, Theodore Ts'o
	<tytso@mit.edu>, "linux-kernel@vger.kernel.org"
	<linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>,
	"linux-nvdimm@ml01.01.org" <linux-nvdimm@ml01.01.org>, Dave Chinner
	<david@fromorbit.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "Andreas
 Dilger" <adilger.kernel@dilger.ca>, Alexander Viro <viro@zeniv.linux.org.uk>,
	Jan Kara <jack@suse.com>, "linux-fsdevel@vger.kernel.org"
	<linux-fsdevel@vger.kernel.org>, "linux-ext4@vger.kernel.org"
	<linux-ext4@vger.kernel.org>
To: Christoph Hellwig <hch@infradead.org>
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From: Christoph Hellwig [mailto:hch@infradead.org]
> On Sat, Sep 10, 2016 at 07:33:18AM +0000, Matthew Wilcox wrote:
> > > caller specific is unaceptable.  That being said your idea doesn't
> > > sounds unreasonable, but will require a bit more work and has no
> > > real short-term need.
> >
> > So your proposal is to remove buffer_heads from ext2?
>=20
> No, the proposal is to remove buffer_heads from XFS first, then GFS2 and =
then
> maybe others like ext4.  I'd like to remove buffer_heads from the DAX pat=
h for
> ext2 and ext4 entitrely for sure (and direct I/O next).

That's ... what I propose.  The only use of buffer_head in my proposal is t=
o
communicate a single extent from the filesystem to the DAX core, and that
can equally well use an iomap.  Ross seems to think that converting the cur=
rent
DAX code over to using iomap requires converting all of ext2 away from
buffer_head; are you saying he's wrong?

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