Re: [RFC v1] io_uring/rsrc: add fast path huge page handling in buffer registration

[David Hildenbrand (Arm)]

On 6/10/26 20:10, Matthew Wilcox wrote:
> On Wed, Jun 10, 2026 at 03:18:52PM +0200, David Hildenbrand (Arm) wrote:
>> On 6/10/26 13:34, Christoph Hellwig wrote:
>>>
>>> I think whatever we're going to use for direct I/O has to also support
>>> non-folio pages, especially PCI P2P memory.  So coming up with an
>>> interface that support this ASAP would be helpful.
>>
>> Yes.
>>
>> I think we can keep returning pages as long a the unpin interface knows the
>> right thing to do to unpin them.
> 
> This would be the get_user_phyrs() interface I've talked about before.
> 
> https://lore.kernel.org/all/ZbVO2RKhw-dLUMvf@xxxxxxxxxxxxxxxxxxxx/
> and the long thread:
> https://lore.kernel.org/all/YdyKWeU0HTv8m7wD@xxxxxxxxxxxxxxxxxxxx/
> 
>> Would there be users for a new interface that returns page ranges as described
>> above, that would want to still unpin stuff partially? E.g., we give them a page
>> range that belongs to the same folio with only a single pin/reference, but they
>> would want to logically split that range and unpin pages individually?
> 
> Urgh, no, we shouldn't do that.  ranges should be pinned / unpinned
> as a whole.  I'm sympathetic to "for this special operation we need to
> create a new range from this existing range and adjust the refcount(s)
> appropriately so each of the two rangees can be put separately", but
> I'm not sympathetic to "we need to allow each page to be individually
> refcounted".

Yes, me too. I wanted to understand if that a common thing to happen for users,
such that we would have to worry about it right from the start.

-- 
Cheers,

David