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Date: Thu, 14 Jun 2018 01:19:47 -0700
From: Christoph Hellwig <hch@infradead.org>
To: NeilBrown <neilb@suse.com>
Cc: Ming Lei <ming.lei@redhat.com>, linux-block@vger.kernel.org,
        dm-devel@redhat.com
Subject: why does __split_and_process_bio use bio_clone_bioset?
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Hi Neil,

In commit 18a25da8 ("dm: ensure bio submission follows a depth-first
tree walk") you've added a call to bio_clone_bioset to
__split_and_process_bio.  Unlike all other bio splitting code this
actually allocates a new bio_vec array instead of just splitting the bio
and the iterator.  I can't actually find a good reason for that either
in a cursory review of the code, the commit or the comments.

Do you remember why this can't just use bio_clone_fast?