[PATCH 2/3] nvme: introduce max_segments controller attribute

[Christoph Hellwig]

On Wed, Aug 16, 2017 at 10:04:09PM +0300, Sagi Grimberg wrote:
>
>>> Why is this needed with patches 1,3 applied?
>>>
>>> We set the page_size and we set max_hw_sectors accordingly.
>>
>> We didn't touch the ctrl->page_size. It's always 4k (the target checks it).
>> This may cause max_segments to be bigger than hw limitation (in PPC for 
>> example).
>
> Right, got confused for a second, but why shouldn't we modify the
> ctrl page_size in rdma? Its not really a controller attribute, but
> rather the local HCA attribute really.

But the controller needs to support it, and NVMe controllers are
only required to support a 4k page size, the rest is optional.

> Or, we could simply fix nvme-core to take PAGE_SIZE if supported by
> the ctrl and fallback to 4k otherwise.

For PCIe (before fabrics existed) we used to do that, but we changed
it for ppc64 in this commit:

c5c9f25b98 ("NVMe: default to 4k device page size")