From: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Subject: Re: [PATCH v2 2/9] ext2: tell DAX the size of allocation holes
Date: Tue, 30 Aug 2016 00:21:29 -0700
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To: Theodore Ts'o <tytso-3s7WtUTddSA@public.gmane.org>, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
 Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
 Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org,
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 Andreas Dilger <adilger.kernel-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org>,
 Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, Jan Kara <jack-IBi9RG/b67k@public.gmane.org>,
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On Mon, Aug 29, 2016 at 08:57:41AM -0400, Theodore Ts'o wrote:
> It's been on my todo list.  The only reason why I haven't done it yet
> is because I knew you were working on a solution, and I didn't want to
> do things one way for buffered I/O, and a different way for Direct
> I/O, and disentangling the DIO code and the different assumptions of
> how different file systems interact with the DIO code is a *mess*.

It is.  I have an almost working iomap direct I/O implementation, which
simplifies a lot of this.  Partially because it expects sane locking
(a shared lock should be held over read, fortunately we now have i_rwsem
for that) and allows less opt-in/out behavior, and partially just
because we have so much better infrastructure now (iomap, bio chaining,
iov_iters, ...).

The iomap version is still work in progress, but I'm about to post
a cut down version for block devices which reduces I/O latency by
20%.