Re: [PATCH v3 5/5] block: use chunk_sectors when evaluating stacked atomic write limits

[John Garry <john.g.garry@oracle.com>]

On 09/07/2025 02:39, Martin K. Petersen wrote:
> The intent for io_min was to convey the physical_block_size in the case
> of an individual drive. And for it to be set to the stripe chunk size in
> stacking scenarios that would otherwise involve read-modify-write (i.e.
> RAID5 and RAID6).
> 
> io_opt was meant to communicate the stripe width. Reporting very large
> values for io_opt is generally counterproductive since we can't write
> multiple gigabytes in a single operation anyway.
> 
> logical <= physical <= io_min <= io_opt <= max_sectors <= max_hw_sectors

Does pbs need to be a power-of-2?

The block queue limits and splitting code seems to rely on that, but it 
is not policed AFAICS.

The stacking code seems to just want it to be a multiple of lbs, which 
itself must be a power-of-2.

Thanks,
John