linux-kernel - Re: [PATCH] block/mq-deadline: Replace DD_PRIO_MAX with DD_PRIO

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Message-ID: <62c9b68f-6adc-41d8-b504-4bce4d721e64@acm.org>
Date: Thu, 28 Aug 2025 21:38:24 -0700
From: Bart Van Assche <bvanassche@....org>
To: chengkaitao <pilgrimtao@...il.com>, axboe@...nel.dk
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 chengkaitao <chengkaitao@...inos.cn>
Subject: Re: [PATCH] block/mq-deadline: Replace DD_PRIO_MAX with DD_PRIO_COUNT

On 8/28/25 6:54 PM, chengkaitao wrote:
> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> index b9b7cdf1d3c9..1a031922c447 100644
> --- a/block/mq-deadline.c
> +++ b/block/mq-deadline.c
> @@ -41,19 +41,16 @@ static const int fifo_batch = 16;       /* # of sequential requests treated as o
>   enum dd_data_dir {
>   	DD_READ		= READ,
>   	DD_WRITE	= WRITE,
> +	DD_DIR_COUNT	= 2
>   };
>   
> -enum { DD_DIR_COUNT = 2 };
> -

This change is not an improvement in my opinion because it makes it
less clear what the role of DD_DIR_COUNT is.

>   enum dd_prio {
> -	DD_RT_PRIO	= 0,
> -	DD_BE_PRIO	= 1,
> -	DD_IDLE_PRIO	= 2,
> -	DD_PRIO_MAX	= 2,
> +	DD_RT_PRIO,
> +	DD_BE_PRIO,
> +	DD_IDLE_PRIO,

There is code that depends on DD_RT_PRIO < DD_BE_PRIO < DD_IDLE_PRIO so 
I'd like to keep the explicit enum values.

> +	DD_PRIO_COUNT
>   };
>   
> -enum { DD_PRIO_COUNT = 3 };

I see the above change as a step backwards because it makes the role of
DD_PRIO_COUNT less clear.

> -	for (prio = DD_BE_PRIO; prio <= DD_PRIO_MAX; prio++) {
> +	for (prio = DD_BE_PRIO; prio < DD_PRIO_COUNT; prio++) {

The current code is easier to read IMHO than the new code.

Thanks,

Bart.