Received-SPF: pass (google.com: domain of linux-kernel+bounces-172066-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Message-ID: <6a50d01a-b5b9-4699-9d58-94e5f8f81c13@gmail.com>
Date: Tue, 7 May 2024 20:35:37 +0100
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [RFC PATCH net-next v8 02/14] net: page_pool: create hooks for
 custom page providers
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Mina Almasry <almasrymina@google.com>,
 Christoph Hellwig <hch@infradead.org>, netdev@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
 linux-alpha@vger.kernel.org, linux-mips@vger.kernel.org,
 linux-parisc@vger.kernel.org, sparclinux@vger.kernel.org,
 linux-trace-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
 bpf@vger.kernel.org, linux-kselftest@vger.kernel.org,
 linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
 "David S. Miller" <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>,
 Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
 Jonathan Corbet <corbet@lwn.net>,
 Richard Henderson <richard.henderson@linaro.org>,
 Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner
 <mattst88@gmail.com>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
 "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
 Helge Deller <deller@gmx.de>, Andreas Larsson <andreas@gaisler.com>,
 Jesper Dangaard Brouer <hawk@kernel.org>,
 Ilias Apalodimas <ilias.apalodimas@linaro.org>,
 Steven Rostedt <rostedt@goodmis.org>, Masami Hiramatsu
 <mhiramat@kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Arnd Bergmann <arnd@arndb.de>, Alexei Starovoitov <ast@kernel.org>,
 Daniel Borkmann <daniel@iogearbox.net>, Andrii Nakryiko <andrii@kernel.org>,
 Martin KaFai Lau <martin.lau@linux.dev>, Eduard Zingerman
 <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
 Yonghong Song <yonghong.song@linux.dev>,
 John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>,
 Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
 Jiri Olsa <jolsa@kernel.org>, Steffen Klassert
 <steffen.klassert@secunet.com>, Herbert Xu <herbert@gondor.apana.org.au>,
 David Ahern <dsahern@kernel.org>,
 Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
 Shuah Khan <shuah@kernel.org>, Sumit Semwal <sumit.semwal@linaro.org>,
 =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
 Amritha Nambiar <amritha.nambiar@intel.com>,
 Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
 Alexander Mikhalitsyn <alexander@mihalicyn.com>,
 Kaiyuan Zhang <kaiyuanz@google.com>, Christian Brauner <brauner@kernel.org>,
 Simon Horman <horms@kernel.org>, David Howells <dhowells@redhat.com>,
 Florian Westphal <fw@strlen.de>, Yunsheng Lin <linyunsheng@huawei.com>,
 Kuniyuki Iwashima <kuniyu@amazon.com>, Jens Axboe <axboe@kernel.dk>,
 Arseniy Krasnov <avkrasnov@salutedevices.com>,
 Aleksander Lobakin <aleksander.lobakin@intel.com>,
 Michael Lass <bevan@bi-co.net>, Jiri Pirko <jiri@resnulli.us>,
 Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
 Lorenzo Bianconi <lorenzo@kernel.org>,
 Richard Gobert <richardbgobert@gmail.com>,
 Sridhar Samudrala <sridhar.samudrala@intel.com>,
 Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
 Johannes Berg <johannes.berg@intel.com>, Abel Wu <wuyun.abel@bytedance.com>,
 Breno Leitao <leitao@debian.org>, David Wei <dw@davidwei.uk>,
 Shailend Chand <shailend@google.com>,
 Harshitha Ramamurthy <hramamurthy@google.com>,
 Shakeel Butt <shakeel.butt@linux.dev>, Jeroen de Borst
 <jeroendb@google.com>, Praveen Kaligineedi <pkaligineedi@google.com>
References: <20240403002053.2376017-3-almasrymina@google.com>
 <ZjH1QaSSQ98mw158@infradead.org>
 <CAHS8izM0=xc2UhUxhnF_BixuFs5VaDV9W1jbso1K+Rg=35NzeA@mail.gmail.com>
 <ZjjHUh1eINPg1wkn@infradead.org>
 <20b1c2d9-0b37-414c-b348-89684c0c0998@gmail.com>
 <20240507161857.GA4718@ziepe.ca> <ZjpVfPqGNfE5N4bl@infradead.org>
 <CAHS8izPH+sRLSiZ7vbrNtRdHrFEf8XQ61XAyHuxRSL9Jjy8YbQ@mail.gmail.com>
 <20240507164838.GG4718@ziepe.ca>
 <0d5da361-cc7b-46e9-a635-9a7a4c208444@gmail.com>
 <20240507175644.GJ4718@ziepe.ca>
Content-Language: en-US
From: Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <20240507175644.GJ4718@ziepe.ca>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit

On 5/7/24 18:56, Jason Gunthorpe wrote:
> On Tue, May 07, 2024 at 06:25:52PM +0100, Pavel Begunkov wrote:
>> 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.
> 
> Sure, but that doesn't mean you can't use dma buf for the other parts
> of the flow. The per-page lifetime is a different topic than the
> refcounting and access of the entire bulk of memory.

Ok, so if we're leaving uapi (and ops) and keep per page/sub-buffer as
is, the rest is resolving uptr -> pages, and passing it to page pool in
a convenient to page pool format (net_iov). I don't see how dmabuf would
help here. Adding dmabuf in the middle (internally wrapping pages) would
add more setup code with the same final result, that is a format that
page pool can work with. And for io_uring it's normal user memory. We'll
have to use dmabuf when we'd want to extend to peer-to-peer and all that
fun, but that's a small fraction of it, and we'll hopefully reuse some
setup helpers from devmem tcp.

-- 
Pavel Begunkov