>    2) It will not scan PTE tables under non-leaf PMD entries that do not
>       have the accessed bit set, when
>       CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG=y.

This assumes  that workloads have reasonable locality. Could there
be a worst case where only one or two pages in each PTE are used,
so this PTE skipping trick doesn't work?

-Andi