Re: [PATCH 3/7] iomap: add bioset in iomap_read_folio_ops for filesystems to use own bioset

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Feb 03, 2025 at 10:43:07AM +0100, Christoph Hellwig wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> Allocate the bio from the bioset provided in iomap_read_folio_ops.
> If no bioset is provided, fs_bio_set is used which is the standard
> bioset for filesystems.
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>

I feel like I've seen this patch and the last one floating around for
quite a while; would you and/or Goldwyn like to merge it for 6.15?

--D

> [hch: factor out two helpers]
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/iomap/buffered-io.c | 51 ++++++++++++++++++++++++++++--------------
>  include/linux/iomap.h  |  6 +++++
>  2 files changed, 40 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 804527dcc9ba..eaffa23eb8e4 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -364,6 +364,39 @@ static inline bool iomap_block_needs_zeroing(const struct iomap_iter *iter,
>  		pos >= i_size_read(iter->inode);
>  }
>  
> +static struct bio_set *iomap_read_bio_set(struct iomap_readpage_ctx *ctx)
> +{
> +	if (ctx->ops && ctx->ops->bio_set)
> +		return ctx->ops->bio_set;
> +	return &fs_bio_set;
> +}
> +
> +static struct bio *iomap_read_alloc_bio(const struct iomap_iter *iter,
> +		struct iomap_readpage_ctx *ctx, loff_t length)
> +{
> +	unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
> +	struct block_device *bdev = iter->iomap.bdev;
> +	struct bio_set *bio_set = iomap_read_bio_set(ctx);
> +	gfp_t gfp = mapping_gfp_constraint(iter->inode->i_mapping, GFP_KERNEL);
> +	gfp_t orig_gfp = gfp;
> +	struct bio *bio;
> +
> +	if (ctx->rac) /* same as readahead_gfp_mask */
> +		gfp |= __GFP_NORETRY | __GFP_NOWARN;
> +
> +	bio = bio_alloc_bioset(bdev, bio_max_segs(nr_vecs), REQ_OP_READ, gfp,
> +			bio_set);
> +
> +	/*
> +	 * If the bio_alloc fails, try it again for a single page to avoid
> +	 * having to deal with partial page reads.  This emulates what
> +	 * do_mpage_read_folio does.
> +	 */
> +	if (!bio)
> +		bio = bio_alloc_bioset(bdev, 1, REQ_OP_READ, orig_gfp, bio_set);
> +	return bio;
> +}
> +
>  static void iomap_read_submit_bio(const struct iomap_iter *iter,
>  		struct iomap_readpage_ctx *ctx)
>  {
> @@ -411,27 +444,11 @@ static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
>  	if (!ctx->bio ||
>  	    bio_end_sector(ctx->bio) != sector ||
>  	    !bio_add_folio(ctx->bio, folio, plen, poff)) {
> -		gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
> -		gfp_t orig_gfp = gfp;
> -		unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
> -
>  		if (ctx->bio)
>  			iomap_read_submit_bio(iter, ctx);
>  
>  		ctx->bio_start_pos = offset;
> -		if (ctx->rac) /* same as readahead_gfp_mask */
> -			gfp |= __GFP_NORETRY | __GFP_NOWARN;
> -		ctx->bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs),
> -				     REQ_OP_READ, gfp);
> -		/*
> -		 * If the bio_alloc fails, try it again for a single page to
> -		 * avoid having to deal with partial page reads.  This emulates
> -		 * what do_mpage_read_folio does.
> -		 */
> -		if (!ctx->bio) {
> -			ctx->bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ,
> -					     orig_gfp);
> -		}
> +		ctx->bio = iomap_read_alloc_bio(iter, ctx, length);
>  		if (ctx->rac)
>  			ctx->bio->bi_opf |= REQ_RAHEAD;
>  		ctx->bio->bi_iter.bi_sector = sector;
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 2930861d1ef1..304be88ecd23 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -311,6 +311,12 @@ struct iomap_read_folio_ops {
>  	 */
>  	void (*submit_io)(struct inode *inode, struct bio *bio,
>  			  loff_t file_offset);
> +
> +	/*
> +	 * Optional, allows filesystem to specify own bio_set, so new bio's
> +	 * can be allocated from the provided bio_set.
> +	 */
> +	struct bio_set *bio_set;
>  };
>  
>  int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops,
> -- 
> 2.45.2
> 
>