Re: [PATCH 11/11] IB/srp: Prevent mapping failures

[Bart Van Assche <bart.vanassche-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org>]

On 04/25/2016 08:53 AM, Leon Romanovsky wrote:
> On Mon, Apr 25, 2016 at 12:46:59PM +0300, Sagi Grimberg wrote:
>>
>>>>>> +		max_max_sectors = (srp_dev->max_pages_per_mr - 1) <<
>>>>>> +				  (ilog2(srp_dev->mr_page_size) - 9);
>>>>>
>>>>>  From my understanding, srp_dev->max_pages_per_mr can be equal to 1, in
>>>>> case device will advertise it.
>>>>>
>>>>> Is this understanding correct?
>>>>> Will the code work in such case?
>>>>
>>>> Hello Leon,
>>>>
>>>> I'm not sure a HCA driver exists for which max_pages_per_mr == 1.
>>>> Additionally, I'm not sure such a driver would be useful because such a
>>>> driver would limit the maximum data transfer size for the iSER protocol to 4
>>>> KB. That is too low to reach good performance.
>>>
>>> Bart and Laurence,
>>> You are raising valuable arguments about sanity of setting srp_dev->max_pages_per_mr
>>> to be equal 1. I totally agree with you that it is insane, however my
>>> original question was "does the code support such value?"
>>
>> I don't see why we should worry about imaginary devices.
>
> It is called corner case and the code supports it.

I can add a WARN_ON_ONCE() statement for max_pages_per_mr == 1. That 
will make it easy to figure out where to start looking if in the future 
a HCA driver would be added that causes max_pages_per_mr == 1.

Bart.
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