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? >> 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()? Regards, Peter Hurley -- 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/
