Hi Nicolin, On Thu, Mar 21, 2019 at 04:32:49PM -0700, Nicolin Chen wrote: > On Tue, Mar 19, 2019 at 02:43:01PM +0000, Catalin Marinas wrote: > > On Tue, Mar 05, 2019 at 10:32:02AM -0800, Nicolin Chen wrote: > > > The addresses within a single page are always contiguous, so it's > > > not so necessary to always allocate one single page from CMA area. > > > Since the CMA area has a limited predefined size of space, it may > > > run out of space in heavy use cases, where there might be quite a > > > lot CMA pages being allocated for single pages. > > > > > > However, there is also a concern that a device might care where a > > > page comes from -- it might expect the page from CMA area and act > > > differently if the page doesn't. > > > > > > This patch tries to get normal pages for single-page allocations > > > unless the device has its own CMA area. This would save resources > > > from the CMA area for more CMA allocations. And it'd also reduce > > > CMA fragmentations resulted from trivial allocations. > > > > This is not sufficient. Some architectures/platforms declare limits on > > the CMA range so that DMA is possible with all expected devices. For > > example, on arm64 we keep the CMA in the lower 4GB of the address range, > > though with this patch you only covered the iommu ops allocation. > > I will follow the way of v1 by adding alloc_page()/free_page() > function to those callers who don't have fallback allocations. > In this way, archs may use different callbacks to alloc pages. > > > Do you have any numbers to back this up? You don't seem to address > > dma_direct_alloc() either but, as I said above, it's not trivial since > > some platforms expect certain physical range for DMA allocations. > > What's the dma_direct_alloc() here about? Mind elaborating?
I just did a grep for dma_alloc_from_contiguous() in the 5.1-rc1 kernel and came up with __dma_direct_alloc_pages(). Should your patch cover this as well? -- Catalin _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
