linux-kernel - Re: [PATCH] blk-iocos: fix inuse clamp when iocg deactivate or free

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Date:   Mon, 16 May 2022 08:37:08 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, duanxiongchun@...edance.com,
        songmuchun@...edance.com
Subject: Re: [PATCH] blk-iocos: fix inuse clamp when iocg deactivate or free

On Mon, May 16, 2022 at 06:19:09PM +0800, Chengming Zhou wrote:
> For an active leaf node, its inuse shouldn't be zero or exceed
> its active, but it's not true when deactivate idle iocg or delete
> iocg in ioc_pd_free().
> 
> Although inuse of 1 is very small, it could cause noticeable hwi
> decrease in the long running server. So we'd better fix it.
> 
> And check iocg->child_active_sum is enough for inner iocg, remove
> the needless list_empty check by the way.

Hey, so, I'm not a fan of these "I read code a bit and thought this could be
changed here and there" patches. There's no theme, overarching direction, or
comprehensive view of the structure. The suggested changes can often be
really subtle, which is likely why it may not seem immediately intuitive on
the first look and triggered the submitter to write up the patch. There's no
practical gain from these changes while there's substantical risk of subtle
breakages.

Here, setting inuse to 1 would cause divide by one in the donation logic and
there are comments about the in the code too. So, nack on the patch, and
plase reconsider your approach to sending patches. The current approach
costs more than helps.

Thanks.

-- 
tejun