Re: [PATCH 21/21] nvme: Support atomic writes

John Garry
2023-10-05T16:19:04Z

On 05/10/2023 14:32, Pankaj Raghav wrote:
>>> te_unit_[min| max]_sectors expects sectors (512 bytes unit)
>>> as input but no conversion is done here from device logical block size
>>> to SECTORs.
>> Yeah, you are right. I think that we can just use:
>>
>> blk_queue_atomic_write_unit_max_sectors(disk->queue,
>> atomic_bs >> SECTOR_SHIFT);
>>
> Makes sense.
> I still don't grok the difference between max_bytes and unit_max_sectors here.
> (Maybe NVMe spec does not differentiate it?)

I think that max_bytes does not need to be a power-of-2 and could be
relaxed.

Having said that, max_bytes comes into play for merging of bios - so if
we are in a scenario with no merging, then may a well leave
atomic_write_max_bytes == atomic_write_unit_max.

But let us check this proposal to relax.

>
> I assume min_sectors should be as follows instead of setting it to 1 (512 bytes)?
>
> blk_queue_atomic_write_unit_min_sectors(disk->queue, bs >> SECTORS_SHIFT);

Yeah, right, we want unit_min to be the logical block size.

Thanks,
John