Re: [PATCH v3 1/9] block: Introduce QUEUE_FLAG_SUB_PAGE_SEGMENTS and CONFIG_BLK_SUB_PAGE_SEGMENTS

[Jens Axboe <axboe@kernel.dk>]

On 1/18/23 3:54 PM, Bart Van Assche wrote:
> Prepare for introducing support for segments smaller than the page size
> by introducing the request queue flag QUEUE_FLAG_SUB_PAGE_SEGMENTS.
> Introduce CONFIG_BLK_SUB_PAGE_SEGMENTS to prevent that performance of
> block drivers that support segments >= PAGE_SIZE would be affected.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Keith Busch <kbusch@kernel.org>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  block/Kconfig          | 9 +++++++++
>  include/linux/blkdev.h | 7 +++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/block/Kconfig b/block/Kconfig
> index 5d9d9c84d516..e85061d2175b 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -35,6 +35,15 @@ config BLOCK_LEGACY_AUTOLOAD
>  	  created on demand, but scripts that manually create device nodes and
>  	  then call losetup might rely on this behavior.
>  
> +config BLK_SUB_PAGE_SEGMENTS
> +       bool "Support segments smaller than the page size"
> +       default n
> +       help
> +	  Most storage controllers support DMA segments larger than the typical
> +	  size of a virtual memory page. Some embedded controllers only support
> +	  DMA segments smaller than the page size. Enable this option to support
> +	  such controllers.

This should not be a visible option at all, affected drivers should just
select it.

-- 
Jens Axboe