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Date:   Tue, 10 Mar 2020 17:38:35 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Omar Sandoval <osandov@osandov.com>
Cc:     linux-btrfs@vger.kernel.org, kernel-team@fb.com,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 12/15] btrfs: get rid of one layer of bios in direct I/O
Message-ID: <20200310163835.GD6361@lst.de>
References: <cover.1583789410.git.osandov@fb.com> <f9d0f9e8b8d11ff103654387f4370f50c6c074ae.1583789410.git.osandov@fb.com>
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On Mon, Mar 09, 2020 at 02:32:38PM -0700, Omar Sandoval wrote:
> 1. The bio created by the generic direct I/O code (dio_bio).
> 2. A clone of dio_bio we create in btrfs_submit_direct() to represent
>    the entire direct I/O range (orig_bio).
> 3. A partial clone of orig_bio limited to the size of a RAID stripe that
>    we create in btrfs_submit_direct_hook().
> 4. Clones of each of those split bios for each RAID stripe that we
>    create in btrfs_map_bio().

Just curious:  what is number 3 useful for?