Re: [PATCH v2 3/5] block: Remove a DMA segment boundary mask check

[Ming Lei <ming.lei@redhat.com>]

On Wed, Mar 25, 2026 at 02:37:13PM -0700, Bart Van Assche wrote:
> Commit d690cb8ae14b ("block: add an API to atomically update queue limits")
> introduced the following code:
> 
>        /*
>         * By default there is no limit on the segment boundary alignment,
>         * but if there is one it can't be smaller than the page size as
>         * that would break all the normal I/O patterns.
>         */
>        if (!lim->seg_boundary_mask)
>                lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
>        if (WARN_ON_ONCE(lim->seg_boundary_mask < PAGE_SIZE - 1))
>                return -EINVAL;
> 
> The comment about "breaking normal I/O patterns" is incorrect - block
> layer code like get_max_segment_size() supports arbitrary boundary mask
> values as long as the boundary mask is not zero. Remove the comment and
> the check because both are confusing.
> 
> This patch prepares for reducing the value of BLK_MIN_SEGMENT_SIZE.
> 
> Fixes: d690cb8ae14b ("block: add an API to atomically update queue limits")
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  block/blk-settings.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 13f5457f9f4e..8538e50afe2c 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -447,15 +447,9 @@ int blk_validate_limits(struct queue_limits *lim)
>  	if (!lim->max_discard_segments)
>  		lim->max_discard_segments = 1;
>  
> -	/*
> -	 * By default there is no limit on the segment boundary alignment,
> -	 * but if there is one it can't be smaller than the page size as
> -	 * that would break all the normal I/O patterns.
> -	 */
> +	/* By default there is no limit on the segment boundary alignment. */
>  	if (!lim->seg_boundary_mask)
>  		lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
> -	if (WARN_ON_ONCE(lim->seg_boundary_mask < BLK_MIN_SEGMENT_SIZE - 1))
> -		return -EINVAL;

Please fold this change into the real code for reducing
BLK_MIN_SEGMENT_SIZE, then it provides consistent handling/view about
->seg_boundary_mask and BLK_MIN_SEGMENT_SIZE.

Thanks,
Ming