Re: [PATCH 2/2] block: support adding less than len in bio_add_hw_page

[Keith Busch <kbusch@kernel.org>]

On Mon, Dec 04, 2023 at 06:34:19PM +0100, Christoph Hellwig wrote:
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index cef830adbc06e0..335d81398991b3 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -966,10 +966,13 @@ int bio_add_hw_page(struct request_queue *q, struct bio *bio,
>  		struct page *page, unsigned int len, unsigned int offset,
>  		unsigned int max_sectors, bool *same_page)
>  {
> +	unsigned int max_size = max_sectors << SECTOR_SHIFT;
> +
>  	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
>  		return 0;
>  
> -	if (((bio->bi_iter.bi_size + len) >> SECTOR_SHIFT) > max_sectors)
> +	len = min3(len, max_size, queue_max_segment_size(q));
> +	if (len > max_size - bio->bi_iter.bi_size)
>  		return 0;
>  
>  	if (bio->bi_vcnt > 0) {

Not related to your patch, but noticed while reviewing: would it not be
beneficial to truncate 'len' down to what can fit in the current-segment
instead of assuming the max segment size?