From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: From: Arnd Bergmann To: linux-arm-kernel@lists.infradead.org Subject: Re: NVMe vs DMA addressing limitations Date: Tue, 10 Jan 2017 16:02:28 +0100 Message-ID: <9020459.Ga31IGQ4TP@wuerfel> In-Reply-To: <20170110144839.GB27156@lst.de> References: <1483044304-2085-1-git-send-email-nikita.yoush@cogentembedded.com> <4137257.d2v87kqLLv@wuerfel> <20170110144839.GB27156@lst.de> MIME-Version: 1.0 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Nikita Yushchenko , Jens Axboe , Sagi Grimberg , linux-pci@vger.kernel.org, Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, Keith Busch , Simon Horman , linux-renesas-soc@vger.kernel.org, Bjorn Helgaas , artemi.ivanov@cogentembedded.com, Christoph Hellwig Content-Type: text/plain; charset="us-ascii" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+bjorn=helgaas.com@lists.infradead.org List-ID: On Tuesday, January 10, 2017 3:48:39 PM CET Christoph Hellwig wrote: > On Tue, Jan 10, 2017 at 12:01:05PM +0100, Arnd Bergmann wrote: > > Another workaround me might need is to limit amount of concurrent DMA > > in the NVMe driver based on some platform quirk. The way that NVMe works, > > it can have very large amounts of data that is concurrently mapped into > > the device. > > That's not really just NVMe - other storage and network controllers also > can DMA map giant amounts of memory. There are a couple aspects to it: > > - dma coherent memoery - right now NVMe doesn't use too much of it, > but upcoming low-end NVMe controllers will soon start to require > fairl large amounts of it for the host memory buffer feature that > allows for DRAM-less controller designs. As an interesting quirk > that is memory only used by the PCIe devices, and never accessed > by the Linux host at all. Right, that is going to become interesting, as some platforms are very limited with their coherent allocations. > - size vs number of the dynamic mapping. We probably want the dma_ops > specify a maximum mapping size for a given device. As long as we > can make progress with a few mappings swiotlb / the iommu can just > fail mapping and the driver will propagate that to the block layer > that throttles I/O. Good idea. Arnd _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel