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([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6aab38b2fc5sm3815784a12.27.2026.09.24.08.53.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Sep 2026 08:53:45 -0700 (PDT) Message-ID: <6d538f3d-dd83-4dfb-b091-9b84acf47c62@gmail.com> Date: Thu, 24 Sep 2026 16:53:40 +0100 Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 06/13] nvme-pci: implement dma-buf backed requests To: Christoph Hellwig Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, Sumit Semwal , =?UTF-8?Q?Christian_K=C3=B6nig?= , Keith Busch , Sagi Grimberg , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , Jens Axboe , Nitesh Shetty , Kanchan Joshi , Anuj Gupta , Tushar Gohad , William Power , Phil Cayton , Matthew Brost , Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Benjamin Marzinski , dm-devel@lists.linux.dev References: <20260922132016.GA30684@lst.de> <20260923045505.GB26231@lst.de> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <20260923045505.GB26231@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/23/26 05:55, Christoph Hellwig wrote: > On Tue, Sep 22, 2026 at 02:37:08PM +0100, Pavel Begunkov wrote: >>> Sashiko had a few comments, which I think are correct - if we use >>> dma_map_sg to map the data, we need to use the sync_sg APIs to >>> transfer ownership. That only matters on non-coherent architectures >>> with MMU, but we need to get it right. >> >> I've seen that and fixed everything locally that should be fixed, >> apart from the sync. I wonder what we can do about that? I can >> somehow replace it with the sg variant for now, but sync'ing the >> entire possibly multi-GB mapping for, let's say, a 512B I/O, sounds >> not wise. > > If we'd want to fix this for real we'd need to add an offset to the > sync by sg methods. Or move away from scatterlists in dma-buf, given > that they are a horrible API. All of these are bigger projects, > though. So for now I think you'd want to do the sync all, and have > the people who run high-performance io_uring code on non-coherent > platforms suffer. > >> And I can think of another place that does mix sync_single >> with sgs. > > Which one? All the recent networking zero-copy / dma-buf apis. -- Pavel Begunkov