linux-kernel - Re: [RFC V4 1/6] blk: prepare to make blk-rq-qos pluggable and modular

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Date:   Thu, 24 Feb 2022 09:51:04 +0800
From:   Wang Jianchao <jianchao.wan9@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Josef Bacik <jbacik@...com>,
        Bart Van Assche <bvanassche@....org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC V4 1/6] blk: prepare to make blk-rq-qos pluggable and
 modular



On 2022/2/24 5:37 上午, Tejun Heo wrote:
> Hello,
> 
>>> We just want to provide the flexibility for the user to open/close a policy
>>> per device. If we need to the policy on a device, we needn't to waste cpu
>> sorry, it should be "If we don't need the policy on a device" ;)
> 
> Yeah, that's what modularization does but why does it need a separate user
> interface for loading? Everything else inits on insmod and exits on rmmod
> and autoloading has been delegated to udev a very long time ago. The
> interface you added for loading module doesn't make sense to me.
> 

The initial version of this patchset has two targets：
(1) Add a sysfs interface to open/close the policy per device. Then we needn't
    waste cpu cycles and memory if the device doesn't need the policy.
(2) Make the policies modular, then it easy to maintain the code of policy in
    production environment as we only need to close the policy and replace the
    .ko file.

The loading module when open policy in sysfs interface is just to avoid modprobe
manually. There is similar operation when switch io scheduler.

And as Christoph suggested, the modularization has been get rid of in next version.

Thanks
Jianchao