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

[Kirill Tkhai]

On 29.03.2022 16:34, Christoph Hellwig wrote:
> 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.

Could you explain what you mean? Why shouldn't I use generic bio merging
code, but implementing my own merging? Which problems you point?

Generic blk-mq is well tested and lots of people work on its performance.
It's not obvious reason I should better implement own realization.