Re: [PATCH] block: Increase BLK_DEF_MAX_SECTORS_CAP

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

On Tue, Jun 17, 2025 at 03:34:30PM +0900, Damien Le Moal wrote:
> Back in 2015, commit d2be537c3ba3 ("block: bump BLK_DEF_MAX_SECTORS to
> 2560") increased the default maximum size of a block device I/O to 2560
> sectors (1280 KiB) to "accommodate a 10-data-disk stripe write with
> chunk size 128k". This choice is rather arbitrary and since then,
> improvements to the block layer have software RAID drivers correctly
> advertize their stripe width through chunk_sectors and abuses of
> BLK_DEF_MAX_SECTORS_CAP by drivers (to set the HW limit rather than the
> default user controlled maximum I/O size) have been fixed.
> 
> Since many block devices can benefit from a larger value of
> BLK_DEF_MAX_SECTORS_CAP, and in particular HDDs, increase this value to
> be 4MiB, or 8192 sectors.
> 
> Suggested-by: Martin K . Petersen <martin.petersen@oracle.com>
> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
> ---
>  include/linux/blkdev.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 85aab8bc96e7..7c35b2462048 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1238,7 +1238,7 @@ enum blk_default_limits {
>   * Not to be confused with the max_hw_sector limit that is entirely
>   * controlled by the driver, usually based on hardware limits.
>   */
> -#define BLK_DEF_MAX_SECTORS_CAP	2560u
> +#define BLK_DEF_MAX_SECTORS_CAP	8192u

The change itself looks good, but the definition should belong to block
layer internal, so why not move it into internal header?


thanks,
Ming