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Date:   Tue, 29 Mar 2022 06:34:13 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Kirill Tkhai <kirill.tkhai@openvz.org>
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Subject: Re: [dm-devel] [PATCH 3/4] dm-qcow2: Introduce driver to create
 block devices over QCOW2 files
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On Mon, Mar 28, 2022 at 02:18:35PM +0300, Kirill Tkhai wrote:
> The driver is request based, since this allows to use blk-mq
> merging of request. Driver splits requests itself, and every
> request (i.e., qio) after splitting fits a single cluster.
> (In some cases it is worth to create bigger splits, and this
> is a subject of further optimizations).

Nak, please don't do that.  If you want finer grained processing use
a bio based driver, not a request based one.  This is just getting us
into tons of problems.