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

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Message-ID: <0d5da361-cc7b-46e9-a635-9a7a4c208444@gmail.com>
Date: Tue, 7 May 2024 18:25:52 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Mina Almasry <almasrymina@...gle.com>
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Subject: Re: [RFC PATCH net-next v8 02/14] net: page_pool: create hooks for
 custom page providers

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