linux-kernel - Re: [PATCH 1/2] loop: use blk_rq_nr_phys_segments() instead of iterating bvecs

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Message-ID: <aRCG3OUThPCys92r@fedora>
Date: Sun, 9 Nov 2025 20:19:40 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Caleb Sander Mateos <csander@...estorage.com>
Cc: Jens Axboe <axboe@...nel.dk>, Damien Le Moal <dlemoal@...nel.org>,
	Christoph Hellwig <hch@....de>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] loop: use blk_rq_nr_phys_segments() instead of
 iterating bvecs

On Sat, Nov 08, 2025 at 04:01:00PM -0700, Caleb Sander Mateos wrote:
> The number of bvecs can be obtained directly from struct request's
> nr_phys_segments field via blk_rq_nr_phys_segments(), so use that
> instead of iterating over the bvecs an extra time.
> 
> Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
> ---
>  drivers/block/loop.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 13ce229d450c..8096478fad45 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -346,16 +346,13 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
>  	struct request *rq = blk_mq_rq_from_pdu(cmd);
>  	struct bio *bio = rq->bio;
>  	struct file *file = lo->lo_backing_file;
>  	struct bio_vec tmp;
>  	unsigned int offset;
> -	int nr_bvec = 0;
> +	unsigned short nr_bvec = blk_rq_nr_phys_segments(rq);
>  	int ret;
>  
> -	rq_for_each_bvec(tmp, rq, rq_iter)
> -		nr_bvec++;
> -

The two may not be same, since one bvec can be splitted into multiple segments.

Thanks,
Ming