Re: [PATCH V10 14/19] block: enable multipage bvecs

[Omar Sandoval]

On Thu, Nov 15, 2018 at 04:53:01PM +0800, Ming Lei wrote:
> This patch pulls the trigger for multi-page bvecs.
> 
> Now any request queue which supports queue cluster will see multi-page
> bvecs.
> 
> Cc: Dave Chinner <dchinner@xxxxxxxxxx>
> Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> Cc: dm-devel@xxxxxxxxxx
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: Shaohua Li <shli@xxxxxxxxxx>
> Cc: linux-raid@xxxxxxxxxxxxxxx
> Cc: linux-erofs@xxxxxxxxxxxxxxxx
> Cc: David Sterba <dsterba@xxxxxxxx>
> Cc: linux-btrfs@xxxxxxxxxxxxxxx
> Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> Cc: linux-xfs@xxxxxxxxxxxxxxx
> Cc: Gao Xiang <gaoxiang25@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Theodore Ts'o <tytso@xxxxxxx>
> Cc: linux-ext4@xxxxxxxxxxxxxxx
> Cc: Coly Li <colyli@xxxxxxx>
> Cc: linux-bcache@xxxxxxxxxxxxxxx
> Cc: Boaz Harrosh <ooo@xxxxxxxxxxxxxxx>
> Cc: Bob Peterson <rpeterso@xxxxxxxxxx>
> Cc: cluster-devel@xxxxxxxxxx
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
>  block/bio.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 6486722d4d4b..ed6df6f8e63d 100644
> --- a/block/bio.c
> +++ b/block/bio.c

This comment above __bio_try_merge_page() doesn't make sense after this
change:

 This is a
 a useful optimisation for file systems with a block size smaller than the
 page size.

Can you please get rid of it in this patch?

> @@ -767,12 +767,24 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
>  
>  	if (bio->bi_vcnt > 0) {
>  		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
> -
> -		if (page == bv->bv_page && off == bv->bv_offset + bv->bv_len) {
> -			bv->bv_len += len;
> -			bio->bi_iter.bi_size += len;
> -			return true;
> -		}
> +		struct request_queue *q = NULL;
> +
> +		if (page == bv->bv_page && off == (bv->bv_offset + bv->bv_len)
> +				&& (off + len) <= PAGE_SIZE)
> +			goto merge;

The parentheses around (bv->bv_offset + bv->bv_len) and (off + len) are
unnecessary noise.

What's the point of the new (off + len) <= PAGE_SIZE check?

> +
> +		if (bio->bi_disk)
> +			q = bio->bi_disk->queue;
> +
> +		/* disable multi-page bvec too if cluster isn't enabled */
> +		if (!q || !blk_queue_cluster(q) ||
> +		    ((page_to_phys(bv->bv_page) + bv->bv_offset + bv->bv_len) !=
> +		     (page_to_phys(page) + off)))

More unnecessary parentheses here.

> +			return false;
> + merge:
> +		bv->bv_len += len;
> +		bio->bi_iter.bi_size += len;
> +		return true;
>  	}
>  	return false;
>  }
> -- 
> 2.9.5
>