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

[Christoph Hellwig <hch@infradead.org>]

On Thu, Feb 12, 2026 at 10:44:44AM +0000, Pavel Begunkov wrote:
> > 
> > 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.

Sure.  But if the application cares that much about TLB pressure
I'd just round up to nice multtiple of PTE levels.

> 
> > 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.

Can you clarify what you mean with 'pbuf'?  The only fixed buffer API I
know is io_uring_register_buffers* which always takes user provided
buffers, so I have a hard time parsing what you're saying there.  But
that might just be sign that I'm no expert in io_uring APIs, and that
web searches have degraded to the point of not being very useful
anymore.