Re: [RFC PATCH net-next v8 02/14] net: page_pool: create hooks for custom page providers

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On 5/7/24 17:48, Jason Gunthorpe wrote:
On Tue, May 07, 2024 at 09:42:05AM -0700, Mina Almasry wrote:

1. Align with devmem TCP to use udmabuf for your io_uring memory. I
think in the past you said it's a uapi you don't link but in the face
of this pushback you may want to reconsider.

dmabuf does not force a uapi, you can acquire your pages however you
want and wrap them up in a dmabuf. No uapi at all.

The point is that dmabuf already provides ops that do basically what
is needed here. We don't need ops calling ops just because dmabuf's
ops are not understsood or not perfect. Fixup dmabuf.

Those ops, for example, are used to efficiently return used buffers
back to the kernel, which is uapi, I don't see how dmabuf can be
fixed up to cover it.

If io_uring wants to take its existing memory pre-registration it can
wrap that in a dmbauf, and somehow pass it to the netstack. Userspace
doesn't need to know a dmabuf is being used in the background.

io_uring's pre-registered memory is just pages, but even that is
going to be replaced with just a normal user buffer pointer.
Regardless, io_uring can wrap pages into a dmabuf, but it's not
a direct replacement for the ops, it'd mandate uapi change in a not
desirable way.

Pavel Begunkov

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