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Subject: Re: [PATCH] bcache: remove the redundant judgment on bi_size
To:     Fengfei Xi <xi.fengfei@h3c.com>
Cc:     linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org,
        kent.overstreet@gmail.com
References: <20210829044947.14703-1-xi.fengfei@h3c.com>
From:   Coly Li <colyli@suse.de>
Message-ID: <be10bf36-5a99-f441-767f-23e76a96aa73@suse.de>
Date:   Sun, 29 Aug 2021 15:49:44 +0800
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On 8/29/21 12:49 PM, Fengfei Xi wrote:
> The bi_size is unsigned int type data not less than 0,
> so we can directly add bi_size without extra judgment
>
> Signed-off-by: Fengfei Xi <xi.fengfei@h3c.com>

NACK. The check is necessary to avoid redundant and unnecessary memory 
write.

Coly Li

> ---
>   drivers/md/bcache/request.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index 6d1de889b..2788eec3a 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -423,9 +423,7 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio)
>   	add_sequential(task);
>   	i->sequential = 0;
>   found:
> -	if (i->sequential + bio->bi_iter.bi_size > i->sequential)
> -		i->sequential	+= bio->bi_iter.bi_size;
> -
> +	i->sequential		+= bio->bi_iter.bi_size;
>   	i->last			 = bio_end_sector(bio);
>   	i->jiffies		 = jiffies + msecs_to_jiffies(5000);
>   	task->sequential_io	 = i->sequential;