Re: [PATCH 15/19] xfs: simplify xfs_buf_submit_bio

On Wed, Apr 30, 2025 at 04:21:45PM -0500, Christoph Hellwig wrote:
> Convert the __bio_add_page(..., virt_to_page(), ...) pattern to the
> bio_add_virt_nofail helper implementing it and use bio_add_vmalloc
> to insulate xfs from the details of adding vmalloc memory to a bio.
> 
> Signed-off-by: Christoph Hellwig <[email protected]>
> ---
>  fs/xfs/xfs_buf.c | 43 ++++++++-----------------------------------
>  1 file changed, 8 insertions(+), 35 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 1a2b3f06fa71..f2d00774a84f 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1333,45 +1333,18 @@ static void
>  xfs_buf_submit_bio(
>  	struct xfs_buf		*bp)
>  {
> +	unsigned int		len = BBTOB(bp->b_length);
> +	unsigned int		nr_vecs = bio_add_max_vecs(bp->b_addr, len);
>  	unsigned int		map = 0;
>  	struct blk_plug		plug;
>  	struct bio		*bio;
>  
> -	if (is_vmalloc_addr(bp->b_addr)) {
> -		unsigned int	size = BBTOB(bp->b_length);
> -		unsigned int	alloc_size = roundup(size, PAGE_SIZE);
> -		void		*data = bp->b_addr;
> -
> -		bio = bio_alloc(bp->b_target->bt_bdev, alloc_size >> PAGE_SHIFT,
> -				xfs_buf_bio_op(bp), GFP_NOIO);
> -
> -		do {
> -			unsigned int	len = min(size, PAGE_SIZE);
> -
> -			ASSERT(offset_in_page(data) == 0);
> -			__bio_add_page(bio, vmalloc_to_page(data), len, 0);
> -			data += len;
> -			size -= len;
> -		} while (size);
> -
> -		flush_kernel_vmap_range(bp->b_addr, alloc_size);
> -	} else {
> -		/*
> -		 * Single folio or slab allocation.  Must be contiguous and thus
> -		 * only a single bvec is needed.
> -		 *
> -		 * This uses the page based bio add helper for now as that is
> -		 * the lowest common denominator between folios and slab
> -		 * allocations.  To be replaced with a better block layer
> -		 * helper soon (hopefully).
> -		 */
> -		bio = bio_alloc(bp->b_target->bt_bdev, 1, xfs_buf_bio_op(bp),
> -				GFP_NOIO);
> -		__bio_add_page(bio, virt_to_page(bp->b_addr),
> -				BBTOB(bp->b_length),
> -				offset_in_page(bp->b_addr));
> -	}
> -
> +	bio = bio_alloc(bp->b_target->bt_bdev, nr_vecs, xfs_buf_bio_op(bp),
> +			GFP_NOIO);
> +	if (is_vmalloc_addr(bp->b_addr))
> +		bio_add_vmalloc(bio, bp->b_addr, len);

I wonder, do we need a debug assertion on the return value?  AFAICT,
bio_add_max_vecs should result in a bio that's big enough to handle the
vmalloc area, but those could be famous last words. :P

Other than that, the code is much cleaner than before. :)

--D

> +	else
> +		bio_add_virt_nofail(bio, bp->b_addr, len);
>  	bio->bi_private = bp;
>  	bio->bi_end_io = xfs_buf_bio_end_io;
>  
> -- 
> 2.47.2
> 
>