On 2020/05/14 12:40, Keith Busch wrote:
> On Thu, May 14, 2020 at 10:54:52AM +0900, Damien Le Moal wrote:
>> Currently, a namespace io_opt queue limit is set by default to the
>> physical sector size of the namespace and to the the write optimal
>> size (NOWS) when the namespace reports this value. This causes problems
>> with block limits stacking in blk_stack_limits() when a namespace block
>> device is combined with an HDD which generally do not report any optimal
>> transfer size (io_opt limit is 0). The code:
>>
>> /* Optimal I/O a multiple of the physical block size? */
>> if (t->io_opt & (t->physical_block_size - 1)) {
>> t->io_opt = 0;
>> t->misaligned = 1;
>> ret = -1;
>> }
>>
>> results in blk_stack_limits() to return an error when the combined
>> devices have different but compatible physical sector sizes (e.g. 512B
>> sector SSD with 4KB sector disks).
>>
>> Fix this by not setting the optiomal IO size limit if the namespace does
>> not report an optimal write size value.
>
> Won't this continue to break if a controller does report NOWS that's not
> a multiple of the physical block size of the device it's stacking with?
When io_opt stacking is handled, the physical sector size for the stacked device
is already resolved to a common value. If the NOWS value cannot accommodate this
resolved physical sector size, this is an incompatible stacking, so failing is
OK in that case.
--
Damien Le Moal
Western Digital Research
