2014-09-30 23:34 GMT+09:00 Peter Hurley <pe...@hurleysoftware.com>: > On 09/29/2014 10:32 AM, Akinobu Mita wrote: >> 2014-09-29 21:09 GMT+09:00 Peter Hurley <pe...@hurleysoftware.com>: >>> On 09/27/2014 08:31 PM, Akinobu Mita wrote: >>>> 2014-09-27 23:30 GMT+09:00 Peter Hurley <pe...@hurleysoftware.com>: >>>>> On 04/15/2014 09:08 AM, Akinobu Mita wrote: >>>>>> This patch set enhances the DMA Contiguous Memory Allocator on x86. >>> >>> [...] >>> >>>>> What this patchset does is restrict all iommu configurations which can >>>>> map all of system memory to one _very_ small physical region, thus >>>>> disabling >>>>> the whole point of an iommu. >>>>> >>>>> Now I know why my GPU is causing paging to disk! And why my RAID >>>>> controller >>>>> stalls for ages when I do a git log at the same time as a kernel build! >>>> >>>> The solution I have for this is that instead of trying to >>>> dma_alloc_from_contiguous() firstly, call alloc_pages() in >>>> dma_alloc_coherent(). >>>> dma_alloc_from_contiguous() should be called only when alloc_pages() is >>>> failed >>>> or DMA_ATTR_FORCE_CONTIGUOUS is specified in dma_attr. >>> >>> Why is all this extra complexity being added when there are no X86 users >>> of DMA_ATTR_FORCE_CONTIGUOUS? >> >> I misunderstood DMA_ATTR_FORCE_CONTIGUOUS. It is specified to request >> that underlaying DMA mapping span physically contiguous with IOMMU. >> But current alloc_dma_coherent() for intel-iommu always returns >> physically contiguous memory, so it is ignored on x86. >> >>>>> And the apparent goal of this patchset is to enable DMA allocation below >>>>> 4GB, which is already supported in the existing page allocator with the >>>>> GFP_DMA32 flag?! >>>> >>>> The goal of this patchset is to enable huge DMA allocation which >>>> alloc_pages() can't (> MAX_ORDER) for the devices that require it. >>> >>> What x86 devices need > MAX_ORDER DMA allocation and why can't they allocate >>> directly from dma_alloc_from_contiguous()? >> >> I need this for UFS unified memory extension which is apparently not in >> mainline for now. >> http://www.jedec.org/standards-documents/docs/jesd220-1 >> http://www.jedec.org/sites/default/files/T_Fujisawa_MF_2013.pdf >> >> But there must be some other use cases on x86, too. Because I have >> received several emails privately from developers who care its status. >> >> And allocating directly from dma_alloc_from_contiguous() in the driver >> doesn't work with IOMMU, as it just returns memory regoin and doesn't >> create DMA mapping. > > > I read the UFS Unified Memory Extension v1.0 (JESD220-1) specification and > it is not clear to me that using DMA mapping is the right approach to > supporting UM, at least on x86.
Without DMA mapping, there is no way for the devices to access host memory. Unified memory extension requires a single contiguous memory region instead of multiple scattered mapping. > And without a mainline user, the merits of this approach are not evident. > I cannot even find a production x86 UFS controller, much less one that > supports UME. > > The only PCI UFS controller I could find (and that mainline supports) is > Samsung's x86 FPGA-based test unit for developing UFS devices in a x86 test > environment, and not a production x86 design. > > Samsung's own roadmap > (http://www.slideshare.net/linaroorg/next-gen-mobilestorageufs) > mentions nothing about bringing UFS to x86 designs. > > Unless there's something else I've missed, I don't think these patches > belong in mainline. Removing CONFIG_CMA_DMA support from x86_64 will disappoint me, but it's personal opinion. FWIW, MIPS also starts supporting it in linux-next. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
