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. -- 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/
