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Message-ID: <ZjxV4yEYXRGElrsA@infradead.org> Date: Wed, 8 May 2024 21:49:39 -0700 From: Christoph Hellwig <hch@...radead.org> To: Pavel Begunkov <asml.silence@...il.com> Cc: Christoph Hellwig <hch@...radead.org>, Jason Gunthorpe <jgg@...pe.ca>, Mina Almasry <almasrymina@...gle.com>, 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>, Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <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>, Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <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>, Christian König <christian.koenig@....com>, Amritha Nambiar <amritha.nambiar@...el.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Alexander Mikhalitsyn <alexander@...alicyn.com>, Kaiyuan Zhang <kaiyuanz@...gle.com>, Christian Brauner <brauner@...nel.org>, Simon Horman <horms@...nel.org>, David Howells <dhowells@...hat.com>, Florian Westphal <fw@...len.de>, Yunsheng Lin <linyunsheng@...wei.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, Jens Axboe <axboe@...nel.dk>, Arseniy Krasnov <avkrasnov@...utedevices.com>, Aleksander Lobakin <aleksander.lobakin@...el.com>, Michael Lass <bevan@...co.net>, Jiri Pirko <jiri@...nulli.us>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Lorenzo Bianconi <lorenzo@...nel.org>, Richard Gobert <richardbgobert@...il.com>, Sridhar Samudrala <sridhar.samudrala@...el.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Johannes Berg <johannes.berg@...el.com>, Abel Wu <wuyun.abel@...edance.com>, Breno Leitao <leitao@...ian.org>, David Wei <dw@...idwei.uk>, 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 Wed, May 08, 2024 at 06:02:14PM +0100, Pavel Begunkov wrote: > Well, the example fell flat, but you don't use dmabuf when there are > no upsides from using it. For instance, when you already have pinned > pages, you're going to use pages, and there are no other refcounting > concerns. Sure. > Unless there is an advantage of dmabufs over FOLL_LONGTERM > that I don't know about when used with normal user pages. The advantages of using a dma-buf over FOLL_LONGTERM are: a) you pre-dma map, which is a significant performance advantage for IOMMU-based setups b) you support any dma-buf exported and not just user memory. This is primarily important for PCIe P2P, but there might be other useful exporters as well > > wish io_uring would have just implemented them from the start instead of > > the current fixed buffers that are not quite as useful by not > > pre-mapping DMA and not supporting P2P. > > fdget(dmabuf) would be horrible, I assume that's not the suggestion. I'm not even sure what you mean with that.
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