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Fri, 6 Jun 2025 17:52:54 +0800 Received: from a010.hihonor.com ([fe80::7127:3946:32c7:6e]) by a010.hihonor.com ([fe80::7127:3946:32c7:6e%14]) with mapi id 15.02.1544.011; Fri, 6 Jun 2025 17:52:54 +0800 From: wangtao To: Christoph Hellwig , =?iso-8859-1?Q?Christian_K=F6nig?= CC: "sumit.semwal@linaro.org" , "kraxel@redhat.com" , "vivek.kasireddy@intel.com" , "viro@zeniv.linux.org.uk" , "brauner@kernel.org" , "hughd@google.com" , "akpm@linux-foundation.org" , "amir73il@gmail.com" , "benjamin.gaignard@collabora.com" , "Brian.Starkey@arm.com" , "jstultz@google.com" , "tjmercier@google.com" , "jack@suse.cz" , "baolin.wang@linux.alibaba.com" , "linux-media@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "linaro-mm-sig@lists.linaro.org" , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "wangbintian(BintianWang)" , yipengxiang , liulu 00013167 , hanfeng 00012985 Subject: RE: [PATCH v4 0/4] Implement dmabuf direct I/O via copy_file_range Thread-Topic: [PATCH v4 0/4] Implement dmabuf direct I/O via copy_file_range Thread-Index: AQHb1G1ol+FT389RFkuW+lwB3adoKrPw4BKAgAADywCAAAF8AIAE6kCg Date: Fri, 6 Jun 2025 09:52:54 +0000 Message-ID: <5d36abace6bf492aadd847f0fabc38be@honor.com> References: <20250603095245.17478-1-tao.wangtao@honor.com> <09c8fb7c-a337-4813-9f44-3a538c4ee8b1@amd.com> In-Reply-To: Accept-Language: zh-CN, en-US Content-Language: zh-CN X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.163.18.240] Content-Type: text/plain; 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wangtao > ; sumit.semwal@linaro.org; kraxel@redhat.com; > vivek.kasireddy@intel.com; viro@zeniv.linux.org.uk; brauner@kernel.org; > hughd@google.com; akpm@linux-foundation.org; amir73il@gmail.com; > benjamin.gaignard@collabora.com; Brian.Starkey@arm.com; > jstultz@google.com; tjmercier@google.com; jack@suse.cz; > baolin.wang@linux.alibaba.com; linux-media@vger.kernel.org; dri- > devel@lists.freedesktop.org; linaro-mm-sig@lists.linaro.org; linux- > kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org; linux- > mm@kvack.org; wangbintian(BintianWang) ; > yipengxiang ; liulu 00013167 > ; hanfeng 00012985 > Subject: Re: [PATCH v4 0/4] Implement dmabuf direct I/O via > copy_file_range >=20 > On Tue, Jun 03, 2025 at 03:14:20PM +0200, Christian K=F6nig wrote: > > On 6/3/25 15:00, Christoph Hellwig wrote: > > > This is a really weird interface. No one has yet to explain why > > > dmabuf is so special that we can't support direct I/O to it when we > > > can support it to otherwise exotic mappings like PCI P2P ones. > > > > With udmabuf you can do direct I/O, it's just inefficient to walk the > > page tables for it when you already have an array of all the folios. >=20 > Does it matter compared to the I/O in this case? >=20 > Either way there has been talk (in case of networking implementations) th= at > use a dmabuf as a first class container for lower level I/O. > I'd much rather do that than adding odd side interfaces. I.e. have a ver= sion > of splice that doesn't bother with the pipe, but instead just uses in-ker= nel > direct I/O on one side and dmabuf-provided folios on the other. If the VFS layer recognizes dmabuf type and acquires its sg_table and folios, zero-copy could also be achieved. I initially thought dmabuf acts as a driver and shouldn't be handled by VFS, so I made dmabuf implement copy_file_range callbacks to support direct I/O zero-copy. I'm open to both approaches. What's the preference of VFS experts? Regards, Wangtao.