== Graceful fallback ==
Code walking pagetables but unware about huge pmds can simply call
-split_huge_page_pmd(mm, pmd) where the pmd is the one returned by
+split_huge_page_pmd(vma, addr, pmd) where the pmd is the one returned by
pmd_offset. It's trivial to make the code transparent hugepage aware
by just grepping for "pmd_offset" and adding split_huge_page_pmd where
missing after pmd_offset returns the pmd. Thanks to the graceful
return NULL;
pmd = pmd_offset(pud, addr);
-+ split_huge_page_pmd(mm, pmd);
++ split_huge_page_pmd(vma, addr, pmd);
if (pmd_none_or_clear_bad(pmd))
return NULL;