linux-kernel - Re: [PATCH -next 1/6] blk-wbt: fix that wbt can't be disabled by default

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Message-ID: <20230511151919.GA7880@lst.de>
Date:   Thu, 11 May 2023 17:19:19 +0200
From:   Christoph Hellwig <hch@....de>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     hch@....de, tj@...nel.org, josef@...icpanda.com, axboe@...nel.dk,
        yukuai3@...wei.com, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH -next 1/6] blk-wbt: fix that wbt can't be disabled by
 default

On Thu, May 11, 2023 at 09:45:04AM +0800, Yu Kuai wrote:
> @@ -730,8 +730,9 @@ void wbt_enable_default(struct gendisk *disk)
>  {
>  	struct request_queue *q = disk->queue;
>  	struct rq_qos *rqos;
> -	bool disable_flag = q->elevator &&
> -		    test_bit(ELEVATOR_FLAG_DISABLE_WBT, &q->elevator->flags);
> +	bool disable_flag = (q->elevator &&
> +		    test_bit(ELEVATOR_FLAG_DISABLE_WBT, &q->elevator->flags)) ||
> +		    !IS_ENABLED(CONFIG_BLK_WBT_MQ);

Not really new in your patch, but I find the logic here very confusing.
First the disable_flag really should be enable instead, as that's how
it's actually checked, and then spelling out the conditions a bit more
would really help readability.  E.g.

	bool enabled = IS_ENABLED(CONFIG_BLK_WBT_MQ);

	if (q->elevator &&
	    test_bit(ELEVATOR_FLAG_DISABLE_WBT, &q->elevator->flags))
		enable = false;