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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>
Cc: Christoph Hellwig <hch@...radead.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-alpha@...r.kernel.org, linux-mips@...r.kernel.org,
 linux-parisc@...r.kernel.org, sparclinux@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
 bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Jonathan Corbet <corbet@....net>,
 Richard Henderson <richard.henderson@...aro.org>,
 Ivan Kokshaysky <ink@...assic.park.msu.ru>, Matt Turner
 <mattst88@...il.com>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
 Helge Deller <deller@....de>, Andreas Larsson <andreas@...sler.com>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 Ilias Apalodimas <ilias.apalodimas@...aro.org>,
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 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Arnd Bergmann <arnd@...db.de>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
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 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Steffen Klassert
 <steffen.klassert@...unet.com>, Herbert Xu <herbert@...dor.apana.org.au>,
 David Ahern <dsahern@...nel.org>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Shuah Khan <shuah@...nel.org>, Sumit Semwal <sumit.semwal@...aro.org>,
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 Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
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 Kaiyuan Zhang <kaiyuanz@...gle.com>, Christian Brauner <brauner@...nel.org>,
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 Florian Westphal <fw@...len.de>, Yunsheng Lin <linyunsheng@...wei.com>,
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 Arseniy Krasnov <avkrasnov@...utedevices.com>,
 Aleksander Lobakin <aleksander.lobakin@...el.com>,
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 Lorenzo Bianconi <lorenzo@...nel.org>,
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 Shailend Chand <shailend@...gle.com>,
 Harshitha Ramamurthy <hramamurthy@...gle.com>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Jeroen de Borst
 <jeroendb@...gle.com>, Praveen Kaligineedi <pkaligineedi@...gle.com>
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

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