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Wed, 7 Oct 2020 12:33:56 +0000 (GMT) Subject: Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM To: Daniel Vetter Cc: Jason Gunthorpe , DRI Development , LKML , Daniel Vetter , Andrew Morton , John Hubbard , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jan Kara , Dan Williams , Linux MM , Linux ARM , Pawel Osciak , Kyungmin Park , Tomasz Figa , Inki Dae , Joonyoung Shim , Seung-Woo Kim , linux-samsung-soc , "open list:DMA BUFFER SHARING FRAMEWORK" , Oded Gabbay From: Marek Szyprowski Message-ID: <725819e9-4f07-3f04-08f8-b6180406b339@samsung.com> Date: Wed, 7 Oct 2020 14:33:56 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: Content-Transfer-Encoding: 7bit Content-Language: en-US X-Brightmail-Tracker: H4sIAAAAAAAAA01SfUzMcRz2vd9rty7fDuuzGHNTI5Twxxdp3saPzZY/bNjI0W8V3ZU7ReYl RXEKC+uc0ivR6uJ0pUYjdKi4JOSltGJlruiwiZWun+i/5/N5nuf7PJ/ty1PKfNabj9TuFnVa dZSKldPltT+fzi63Hgid8yt3KsksLWZJxjk7Irnt7yhSWG+myPPvvSxJbztNkwsZSTJy3vgQ DaEuGbn+IY8jXa2NNGlI/MwRS8cLhjRVZbIk9ZqVIa3FgwwxPq2WEXvXG4acdfzkiPFMN0uc RwfYJROECwmNtHD7Rw4tVJrecUL+rW6ZYOlL54SHxl+00HbCJhNuFBwS0pJ6WKGjv5sVequb WeFkWRES6nPuc4LTMlmwOt/QIWM3yYPCxKjIOFEXELxVHvEgrxTF3HLf+6AlmUlAKXIDcuMB z4eU1JPIgOS8El9BcM/ioFyEEn9D0NYcLxFOBG/7r7Ejjtb2r4xEFCIoKEhmpaEXwcUvVs6l GocJ5GYny1x4PPaDY4NHaJeIwi0sPM9tHc5gcSAYHIbhZxU4GFIaK4fNNJ4GJqfUYwLeBnX2 RE7SeMKj8520C7vhddBSZmNcmMJToMKRSUnYC153ZstcYYDf85B5qhBJvVdAVlENJeFx8MlW xkl4EgxWjhiSELQ/KeGkIRVBU6Lxr3sRvH3SP1SVH4qYAaVVAdJ6KVw63sO41oA94JXDUyrh AenlGZS0VsCxZKWk9gWTzfwv9q79GXUaqUyjTjONOsc06hzT/9wcRBchLzFWrwkX9fO04h5/ vVqjj9WG+2+P1ljQ0NetG7B9v4mqf2+rQZhHKnfFhl37Q5WMOk4fr6lBwFOq8YplDXVblIow dfw+URcdqouNEvU1aCJPq7wU8/K6NytxuHq3uFMUY0TdCCvj3bwTUEvf1vnxl/tNZuXMoE7z x45dj1amVZQ0RHSsvH2wOXD1qmB3O6VZ89IncX3T3DLvoGjNywVTsf8d3ynLPSDycGfWwB1W u2ojQ4+Z7pa22MCtrlp63KYeXLvQ2hfi3OkT0hNXXx1au+hq1uP6gB0R+5vnZB9cOyvGt6d2 cVig2V6holW0PkId6Efp9Oo/bu17QLYDAAA= X-Brightmail-Tracker: H4sIAAAAAAAAA02Sf0zMYRzH93x/Xq3j6xSPZrJb2Npc7pJ7Is3MeNZimjGLnFPfdU3X5b53 rQxFyC5Z0Y/raqRY1lL0iyxNiQpFpSx2tfRDmatxtCWi69j677W936/n83m2j4iU1NCeouhY A6+PVcdIGVfq5WyLdX1tzWnVhtE8ChVUlDEoN/sNQDcHrSQqeVVOorc/Jhl0dSCDQvm5KQTK M7eCORoj0P2RIhaN9XdSqP3cFxZVDvXSqPtRAYMu36uhUX/ZHxqZXzcQ6M3YBxpl2aZZZL42 ziD7hVlmmwfOT+6k8OOpQgrXWawsLq4fJ3Dlt6ssbjXPUHggrYXAVbeScHrKBIOHfo4zeLKh h8FXqksBflXYzGJ75SpcY/9A7V0cJgvU64wGfrVGJxi2Sg/JkUImD0AyxcYAmdxPGb5Z4S/1 DQqM5GOi43m9b9BRmeZZUQWIq3dLeNZ3kU4Gqa4m4CKC3EbYP/iVNgFXkYS7DaDFaiecwUrY lpNMO3kp/NVrYpwlG4Avpp9SjmAph+DNGxfnBXfOB176c55ylEjOysCBzOL5QMJdo+C7Eexg hpNDk83xkotIzAXB1M461sEU5w0tdhvpYA/uGEzryiKcnSWwLW94fpgLFwr7qlvmNyK5TfB6 1SDpZC/4wFbwj5fD98M3iAwgsSzQLQsUywLFskApBFQpcOeNgjZKKyhkglorGGOjZBE6bSWY O5na59PVD4FpYl8T4ERA6iY+eOKUSkKr44VEbROAIlLqLt7e/vKIRBypTjzJ63UqvTGGF5qA /9znMklPjwjd3AHGGlRyf7kSBciVfkq/TUi6XHyJazws4aLUBv44z8fx+v8eIXLxTAYRwd8P 1H+eXWYryZnR7CgIfhJCTqWH729LHDrzyWtP+miUuaksx12pqJioKon7mL1TnRHR09iVxG73 uFxYxlZL1w4ZX2xpLjffTZts9o4M8xfwrt7u4pC+Fao7qYHh3m/XZf3WJvidXdOxef2Oji91 Iz27VcbdraHjYYNB0bZFxaFSStCo5T6kXlD/BZ+7bo9IAwAA X-CMS-MailID: 20201007123358eucas1p1eccb32143b09c921ae0a4f883164d17d X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20201003094038eucas1p12aaafe0f52a7747bc2ba95ccb91d1651 X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20201003094038eucas1p12aaafe0f52a7747bc2ba95ccb91d1651 References: <20201002175303.390363-1-daniel.vetter@ffwll.ch> <20201002175303.390363-2-daniel.vetter@ffwll.ch> <20201002180603.GL9916@ziepe.ca> <20201002233118.GM9916@ziepe.ca> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Daniel, On 07.10.2020 14:01, Daniel Vetter wrote: > On Wed, Oct 7, 2020 at 12:47 PM Marek Szyprowski > wrote: >> On 03.10.2020 11:40, Daniel Vetter wrote: >>>> After he three places above should use pin_user_pages_fast(), then >>>> this whole broken API should be moved into videobuf2-memops.c and a >>>> big fat "THIS DOESN'T WORK" stuck on it. >>>> >>>> videobuf2 should probably use P2P DMA buf for this instead. >>> Yup this should be done with dma_buf instead, and v4l has that. >> Yes, V4L2 has dma_buf support NOW. That days, using so called V4L2 >> USERPTR method was the only way to achieve zero copy buffer sharing >> between devices, so this is just a historical baggage. I've been >> actively involved in implementing that. I've tried to make it secure as >> much as possible assuming the limitation of that approach. With a few >> assumptions it works fine. Buffers are refcounted both by the >> vm_ops->open or by incrementing the refcount of the vm->file. This >> basically works with any sane driver, which doesn't free the mmaped >> buffer until the file is released. This is true for V4L2 and FBdev devices. > I'm not seeing any of that vm->file refcounting going on, so not > seeing anything that prevents the mmap area from being removed. Can > you pls give me some pointers about which code you're thinking of? Well, it was in vb2_get_vma() function, but now I see that it has been lost in fb639eb39154 and 6690c8c78c74 some time ago... Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland