Re: [PATCH v3 4/6] block: Reduce the minimum value for the maximum DMA segment size

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

On Mon, Mar 30, 2026 at 12:49:33PM -0700, Bart Van Assche wrote:
> On 3/29/26 7:38 AM, Ming Lei wrote:
> > On Fri, Mar 27, 2026 at 02:13:44PM -0700, Bart Van Assche wrote:
> > > All block devices that are supported by the Linux kernel have a DMA engine
> > > that supports DMA segments of 4 KiB or larger. Allow smaller DMA segment
> > > sizes because these are useful for block layer testing. Reject values below
> > 
> > Can you share why/what it is useful just for test purpose?
> 
> Your commit 889c57066cee ("block: make segment size limit workable for >
> 4K PAGE_SIZE") adds support for devices with a maximum segment size
> limit that is less than the virtual memory page size. With
> BLK_MIN_SEGMENT_SIZE == 4096, it is not possible to test the code paths
> added by this commit if PAGE_SIZE == 4096. Allowing a segment size limit
> that is less than 4096 bytes makes it possible to test the new code
> paths on systems with PAGE_SIZE == 4096, e.g. an x86 VM.

lim->min_segment_size is <= PAGE_SIZE and BLK_MIN_SEGMENT_SIZE is same with
4096, so 889c57066cee basically changes nothing for 4096 PAGE_SIZE.

What is the exactly code path you are trying to cover by changing
BLK_MIN_SEGMENT_SIZE?

Thanks, 
Ming