[$] Better hugetlb page-table walking

The kernel must often step through the page tables of one or more processesto carry out various operations. This "page-table walking" tends to beperformed by ad-hoc (duplicated) code all over the kernel. Oscar Salvadorused a memory-management-track session at the 2025 Linux Storage,Filesystem, Memory-Management, and BPF Summit to talk about strategies tounify the kernel's page-table walking code just a little bit by makinghugetlb pages look more like ordinary pages.