linux-kernel - Re: [PATCH] bcache: remove the redundant judgment on bi

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Message-ID: <ed49f33da50e4f5c88f986c8ed239e78@h3c.com>
Date:   Mon, 30 Aug 2021 06:29:45 +0000
From:   Xifengfei <xi.fengfei@....com>
To:     Coly Li <colyli@...e.de>
CC:     "linux-bcache@...r.kernel.org" <linux-bcache@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kent.overstreet@...il.com" <kent.overstreet@...il.com>
Subject: Re: [PATCH] bcache: remove the redundant judgment on bi_size

（Sorry, there was an obvious typo in the last email）
Thanks a lot. I understand the purpose.
So is the original judgment process too complicated?  Can we judge bi_size directly?  This will be more concise

@@ -423,7 +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)
+       if (bio->bi_iter.bi_size)
                i->sequential   += bio->bi_iter.bi_size;

        i->last                  = bio_end_sector(bio);

Thanks
Fengfei

-----邮件原件-----
发件人: Coly Li [mailto:colyli@...e.de]
发送时间: 2021年8月29日 15:50
收件人: xifengfei (RD) <xi.fengfei@....com>
抄送: linux-bcache@...r.kernel.org; linux-kernel@...r.kernel.org; kent.overstreet@...il.com
主题: Re: [PATCH] bcache: remove the redundant judgment on bi_size

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@....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;