[dm-devel] [RFC PATCH 1/3] block: add copy offload support

[Jens Axboe]

On 2/4/22 5:09 AM, Mikulas Patocka wrote:
> 
> 
> On Thu, 3 Feb 2022, Bart Van Assche wrote:
> 
>> On 2/3/22 10:50, Mikulas Patocka wrote:
>>> On Tue, 1 Feb 2022, Bart Van Assche wrote:
>>>> On 2/1/22 10:32, Mikulas Patocka wrote:
>>>>>    /**
>>>>> + * blk_queue_max_copy_sectors - set maximum copy offload sectors for
>>>>> the
>>>>> queue
>>>>> + * @q:  the request queue for the device
>>>>> + * @size:  the maximum copy offload sectors
>>>>> + */
>>>>> +void blk_queue_max_copy_sectors(struct request_queue *q, unsigned int
>>>>> size)
>>>>> +{
>>>>> +	q->limits.max_copy_sectors = size;
>>>>> +}
>>>>> +EXPORT_SYMBOL_GPL(blk_queue_max_copy_sectors);
>>>>
>>>> Please either change the unit of 'size' into bytes or change its type into
>>>> sector_t.
>>>
>>> blk_queue_chunk_sectors, blk_queue_max_discard_sectors,
>>> blk_queue_max_write_same_sectors, blk_queue_max_write_zeroes_sectors,
>>> blk_queue_max_zone_append_sectors also have the unit of sectors and the
>>> argument is "unsigned int". Should blk_queue_max_copy_sectors be
>>> different?
>>
>> As far as I know using the type sector_t for variables that represent a number
>> of sectors is a widely followed convention:
>>
>> $ git grep -w sector_t | wc -l
>> 2575
>>
>> I would appreciate it if that convention would be used consistently, even if
>> that means modifying existing code.
>>
>> Thanks,
>>
>> Bart.
> 
> Changing the sector limit variables in struct queue_limits from
> unsigned int to sector_t would increase the size of the structure and
> its cache footprint.
> 
> And we can't send bios larger than 4GiB anyway because bi_size is
> 32-bit.
> 
> Jens, what do you think about it? Should the sectors limits be
> sector_t?

Why make it larger than it needs to?

-- 
Jens Axboe