linux-kernel - Re: [dm-devel] [PATCH 3/4] dm-qcow2: Introduce driver to create block devices over QCOW2 files

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Message-ID: <YkMK1cmWyEJGoMB+@infradead.org>
Date:   Tue, 29 Mar 2022 06:34:13 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Kirill Tkhai <kirill.tkhai@...nvz.org>
Cc:     agk@...hat.com, snitzer@...hat.com, dm-devel@...hat.com,
        song@...nel.org, linux-kernel@...r.kernel.org,
        khorenko@...tuozzo.com, axboe@...nel.dk,
        linux-block@...r.kernel.org
Subject: Re: [dm-devel] [PATCH 3/4] dm-qcow2: Introduce driver to create
 block devices over QCOW2 files

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.