linux-kernel - Re: [PATCH 0/13] blk: make blk-rq-qos policies pluggable and modular

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Date:   Mon, 10 Jan 2022 19:25:54 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Christoph Hellwig <hch@...radead.org>,
        Wang Jianchao <jianchao.wan9@...il.com>
Cc:     axboe@...nel.dk, jbacik@...com, tj@...nel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/13] blk: make blk-rq-qos policies pluggable and modular

On 1/10/22 09:36, Christoph Hellwig wrote:
> On Mon, Jan 10, 2022 at 05:10:33PM +0800, Wang Jianchao wrote:
>> This patchset attempts to make blk-rq-qos framework pluggable and modular.
> 
> I really don't think making them policies modular is a good thing, and
> your new exports/APIs are a very good sign for why it is not a good
> idea.

Hi Christoph,

Personally I don't need the ability to implement blk-rq-qos 
functionality as a loadable kernel module.

When I implemented the ioprio rq-qos policy (see also blk-ioprio.c) I 
noticed that I had to make changes in the block layer core 
(blkcg_init_queue(), rq_qos_id_to_name(), blk-rq-qos.h) instead of 
having all code related to the new rq-pos policy contained in a single 
file. I think it would be an improvement if new rq-qos policies could be 
implemented in a single source file and no block layer core changes 
would be necessary.

Thanks,

Bart.