Re: [PATCH v4 07/15] iomap: track read/readahead folio ownership internally

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

On Mon, Sep 22, 2025 at 05:23:45PM -0700, Joanne Koong wrote:
> The purpose of "struct iomap_read_folio_ctx->cur_folio_in_bio" is to
> track folio ownership to know who is responsible for unlocking it.
> Rename "cur_folio_in_bio" to "cur_folio_owned" to better reflect this
> purpose and so that this can be generically used later on by filesystems
> that are not block-based.
> 
> Since "struct iomap_read_folio_ctx" will be made a public interface
> later on when read/readahead takes in caller-provided callbacks, track
> the folio ownership state internally instead of exposing it in "struct
> iomap_read_folio_ctx" to make the interface simpler for end users.
> 
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>

Looks good to me now,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/iomap/buffered-io.c | 34 +++++++++++++++++++++++-----------
>  1 file changed, 23 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 09e65771a947..34df1cddf65c 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -362,7 +362,6 @@ static void iomap_read_end_io(struct bio *bio)
>  
>  struct iomap_read_folio_ctx {
>  	struct folio		*cur_folio;
> -	bool			cur_folio_in_bio;
>  	void			*read_ctx;
>  	struct readahead_control *rac;
>  };
> @@ -386,7 +385,6 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
>  	sector_t sector;
>  	struct bio *bio = ctx->read_ctx;
>  
> -	ctx->cur_folio_in_bio = true;
>  	if (ifs) {
>  		spin_lock_irq(&ifs->state_lock);
>  		ifs->read_bytes_pending += plen;
> @@ -423,7 +421,7 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
>  }
>  
>  static int iomap_read_folio_iter(struct iomap_iter *iter,
> -		struct iomap_read_folio_ctx *ctx)
> +		struct iomap_read_folio_ctx *ctx, bool *folio_owned)
>  {
>  	const struct iomap *iomap = &iter->iomap;
>  	loff_t pos = iter->pos;
> @@ -460,6 +458,7 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
>  			folio_zero_range(folio, poff, plen);
>  			iomap_set_range_uptodate(folio, poff, plen);
>  		} else {
> +			*folio_owned = true;
>  			iomap_bio_read_folio_range(iter, ctx, pos, plen);
>  		}
>  
> @@ -482,16 +481,22 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
>  	struct iomap_read_folio_ctx ctx = {
>  		.cur_folio	= folio,
>  	};
> +	/*
> +	 * If an IO helper takes ownership of the folio, it is responsible for
> +	 * unlocking it when the read completes.
> +	 */
> +	bool folio_owned = false;
>  	int ret;
>  
>  	trace_iomap_readpage(iter.inode, 1);
>  
>  	while ((ret = iomap_iter(&iter, ops)) > 0)
> -		iter.status = iomap_read_folio_iter(&iter, &ctx);
> +		iter.status = iomap_read_folio_iter(&iter, &ctx,
> +				&folio_owned);
>  
>  	iomap_bio_submit_read(&ctx);
>  
> -	if (!ctx.cur_folio_in_bio)
> +	if (!folio_owned)
>  		folio_unlock(folio);
>  
>  	/*
> @@ -504,14 +509,15 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
>  EXPORT_SYMBOL_GPL(iomap_read_folio);
>  
>  static int iomap_readahead_iter(struct iomap_iter *iter,
> -		struct iomap_read_folio_ctx *ctx)
> +		struct iomap_read_folio_ctx *ctx,
> +		bool *cur_folio_owned)
>  {
>  	int ret;
>  
>  	while (iomap_length(iter)) {
>  		if (ctx->cur_folio &&
>  		    offset_in_folio(ctx->cur_folio, iter->pos) == 0) {
> -			if (!ctx->cur_folio_in_bio)
> +			if (!*cur_folio_owned)
>  				folio_unlock(ctx->cur_folio);
>  			ctx->cur_folio = NULL;
>  		}
> @@ -519,9 +525,9 @@ static int iomap_readahead_iter(struct iomap_iter *iter,
>  			ctx->cur_folio = readahead_folio(ctx->rac);
>  			if (WARN_ON_ONCE(!ctx->cur_folio))
>  				return -EINVAL;
> -			ctx->cur_folio_in_bio = false;
> +			*cur_folio_owned = false;
>  		}
> -		ret = iomap_read_folio_iter(iter, ctx);
> +		ret = iomap_read_folio_iter(iter, ctx, cur_folio_owned);
>  		if (ret)
>  			return ret;
>  	}
> @@ -554,15 +560,21 @@ void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
>  	struct iomap_read_folio_ctx ctx = {
>  		.rac	= rac,
>  	};
> +	/*
> +	 * If an IO helper takes ownership of the folio, it is responsible for
> +	 * unlocking it when the read completes.
> +	 */
> +	bool cur_folio_owned = false;
>  
>  	trace_iomap_readahead(rac->mapping->host, readahead_count(rac));
>  
>  	while (iomap_iter(&iter, ops) > 0)
> -		iter.status = iomap_readahead_iter(&iter, &ctx);
> +		iter.status = iomap_readahead_iter(&iter, &ctx,
> +					&cur_folio_owned);
>  
>  	iomap_bio_submit_read(&ctx);
>  
> -	if (ctx.cur_folio && !ctx.cur_folio_in_bio)
> +	if (ctx.cur_folio && !cur_folio_owned)
>  		folio_unlock(ctx.cur_folio);
>  }
>  EXPORT_SYMBOL_GPL(iomap_readahead);
> -- 
> 2.47.3
> 
>