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

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Message-ID: <54557a1a-94b5-9f75-61f9-90991d5ff409@gmail.com>
Date:   Fri, 25 Feb 2022 10:02:39 +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 2022/2/25 12:53 上午, Tejun Heo wrote:
> On Thu, Feb 24, 2022 at 10:50:22AM +0800, Wang Jianchao wrote:
>> Yes, right now, every policy has their own way to turn off, but we always need to
>> iterate the rqos list and enter into the policy's callback to check it. And every
>> blkio cgroup needs to allocate memory for it even we don't use it.
>>
>> I don't this patchset is adding a new layer, but blk-rq-qos layer has been already
>> there , we just add a unified interface to open/close the policies.
> 
> We're talking in circles. We already know when a policy is inactive. If it
> sits in hot path in that state, take it off whatever gets iterated in hot
> path and put it back on when it actually gets enabled. The same goes for
> memory allocation. If there's substantial amount of memory allocted while
> not used, make that dynamic and trigger it when the policy starts getting
> used. It makes no sense to add another enable/disable interface on top.
>
It can make things more complicated if we does as above...

> FWIW, please consider the series nacked on this side.

Anyway, thanks so much for all of your comment ;)

Regards
Jianchao