Re: [PATCH v1 03/11] io_uring/kbuf: add support for kernel-managed buffer rings

[Pavel Begunkov <asml.silence@gmail.com>]

On 2/11/26 15:45, Christoph Hellwig wrote:
> On Tue, Feb 10, 2026 at 04:34:47PM +0000, Pavel Begunkov wrote:
>>> +	union {
>>> +		/* used for pbuf rings */
>>> +		__u64	ring_addr;
>>> +		/* used for kmbuf rings */
>>> +		__u32   buf_size;
>>
>> If you're creating a region, there should be no reason why it
>> can't work with user passed memory. You're fencing yourself off
>> optimisations that are already there like huge pages.
> 
> Any pages mapped to userspace can be allocated in the kernel as well.

pow2 round ups will waste memory. 1MB allocations will never
become 2MB huge pages. And there is a separate question of
1GB huge pages. The user can be smarter about all placement
decisions.

> And I really do like this design, because it means we can have a
> buffer ring that is only mapped read-only into userspace.  That way
> we can still do zero-copy raids if the device requires stable pages
> for checksumming or raid.  I was going to implement this as soon
> as this series lands upstream.

That's an interesting case. To be clear, user provided memory is
an optional feature for pbuf rings / regions / etc., and I think
the io_uring uapi should leave fields for the feature. However, I
have nothing against fuse refusing to bind to buffer rings it
doesn't like.

-- 
Pavel Begunkov