On 18.02.25 23:22, Alex Williamson wrote:
follow_pfnmap_start() walks the page table for a given address and fills out the struct follow_pfnmap_args in pfnmap_args_setup(). The address mask of the page table level is already provided to this latter function for calculating the pfn. This address mask can also be useful for the caller to determine the extent of the contiguous mapping. For example, vfio-pci now supports huge_fault for pfnmaps and is able to insert pud and pmd mappings. When we DMA map these pfnmaps, ex. PCI MMIO BARs, we iterate follow_pfnmap_start() to get each pfn to test for a contiguous pfn range. Providing the mapping address mask allows us to skip the extent of the mapping level. Assuming a 1GB pud level and 4KB page size, iterations are reduced by a factor of 256K. In wall clock time, mapping a 32GB PCI BAR is reduced from ~1s to <1ms. Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: linux-mm@xxxxxxxxx Reviewed-by: Peter Xu <peterx@xxxxxxxxxx> Reviewed-by: "Mitchell Augustin" <mitchell.augustin@xxxxxxxxxxxxx> Tested-by: "Mitchell Augustin" <mitchell.augustin@xxxxxxxxxxxxx> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> ---
Acked-by: David Hildenbrand <david@xxxxxxxxxx> -- Cheers, David / dhildenb
