Re: [dm-devel] [PATCH 2/6] dm: open code blk_max_size_offset in max_io_len

[Mike Snitzer <snitzer@kernel.org>]

On Tue, Jun 14 2022 at  5:09P -0400,
Christoph Hellwig <hch@lst.de> wrote:

> max_io_len always passes an explicitly non-zero chunk_sectors into
> blk_max_size_offset.  That means much of blk_max_size_offset is not
> needed and can be open coded to simplify the code.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/md/dm.c | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index d8f16183bf27c..0514358a1f8e5 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1079,23 +1079,18 @@ static sector_t max_io_len(struct dm_target *ti, sector_t sector)
>  {
>  	sector_t target_offset = dm_target_offset(ti, sector);
>  	sector_t len = max_io_len_target_boundary(ti, target_offset);
> -	sector_t max_len;
>  
>  	/*
>  	 * Does the target need to split IO even further?
>  	 * - varied (per target) IO splitting is a tenet of DM; this
>  	 *   explains why stacked chunk_sectors based splitting via
> -	 *   blk_max_size_offset() isn't possible here. So pass in
> -	 *   ti->max_io_len to override stacked chunk_sectors.
> +	 *   blk_queue_split() isn't possible here.
>  	 */
> -	if (ti->max_io_len) {
> -		max_len = blk_max_size_offset(ti->table->md->queue,
> -					      target_offset, ti->max_io_len);
> -		if (len > max_len)
> -			len = max_len;
> -	}
> -
> -	return len;
> +	if (!ti->max_io_len)
> +		return len;
> +	return min_t(sector_t, len,
> +		min(queue_max_sectors(ti->table->md->queue),
> +		    blk_chunk_sectors_left(target_offset, ti->max_io_len)));
>  }
>  
>  int dm_set_target_max_io_len(struct dm_target *ti, sector_t len)
> -- 
> 2.30.2
> 

Not in love with the nested min() but don't have a better suggestion.

Reviewed-by: Mike Snitzer <snitzer@kernel.org>

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