On Wed, 19 Feb 2025 09:31:48 +0100 David Hildenbrand <david@xxxxxxxxxx> wrote: > 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> Thanks, David! Is there any objection from mm folks to bring this in through the vfio tree? Patch: https://lore.kernel.org/all/20250218222209.1382449-6-alex.williamson@xxxxxxxxxx/ Series: https://lore.kernel.org/all/20250218222209.1382449-1-alex.williamson@xxxxxxxxxx/ Thanks, Alex
