Re: [PATCH v2 8/8] null_blk: Support configuring the maximum segment size

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On 12/1/22 07:29, Bart Van Assche wrote:
> On 11/23/22 17:40, Damien Le Moal wrote:
>> On 11/24/22 05:57, Bart Van Assche wrote:
>>> +static unsigned int g_max_segment_size = 1UL << 31;
>>
>> 1UL is unsigned long be this var is unsigned int. Why not simply use
>> UINT_MAX here ? You prefer the 2GB value ? If yes, then may be at least
>> change that to "1U << 31", no ?
>>
>> [ ... ]
>>> @@ -2106,6 +2119,7 @@ static int null_add_dev(struct nullb_device *dev)
>>>   	dev->max_sectors = min_t(unsigned int, dev->max_sectors,
>>>   				 BLK_DEF_MAX_SECTORS);
>>>   	blk_queue_max_hw_sectors(nullb->q, dev->max_sectors);
>>> +	blk_queue_max_segment_size(nullb->q, dev->max_segment_size);
>>
>> Should we keep the ability to use the kernel default value as the default
>> here ?
>> E.g.
>>
>> 	if (dev->max_segment_size)
>> 		blk_queue_max_segment_size(nullb->q,
>> 				dev->max_segment_size);
>>
>> If yes, then g_max_segment_size initial value should be 0, meaning "kernel
>> default".
> 
> Hi Damien,
> 
> How about changing the default value for g_max_segment_size from
> 1UL << 31 into BLK_MAX_SEGMENT_SIZE? That will simplify the code and 
> also prevents that this patch changes the behavior of the null_blk 
> driver if g_max_segment_size is not modified by the user.

Sounds good to me.

> 
> Thanks,
> 
> Bart.
> 

-- 
Damien Le Moal
Western Digital Research




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