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

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Message-ID: <2017d0ad-9e76-d1d9-666a-5f2cd7632b31@gmail.com>
Date:   Tue, 11 Jan 2022 09:53:37 +0800
From:   Wang Jianchao <jianchao.wan9@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     axboe@...nel.dk, jbacik@...com, tj@...nel.org, bvanassche@....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 2022/1/11 1:36 上午, 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.

Actually, before sent out this version,  I didn't make them modular but just
pluggable, and yes, it was because I had to export those interfaces. However,
when I made the patch to introduce a policy which support cgroup and had to
increase the BLKCG_MAX_POLS, it seemed worthy to make the previous policies
modular as we can release the blkcg slot when policy module is not installed.

In addition, our own kernel uses the policies as module. When we recommend iocost
to our customer, they love to see we needn't to reboot machine and even needn't to
stop the IO workload if upgrading of iocost is needed

Thanks
Jianchao