pmd_mkold
pmd = pmdp_xchg_direct(vma->vm_mm, addr, pmdp, pmd_mkold(pmd));
set_pmd_at(vma->vm_mm, address, pmdp, pmd_mkold(pmd));
WARN_ON(!pmd_young(pmd_mkyoung(pmd_mkold(pmd))));
WARN_ON(pmd_young(pmd_mkold(pmd_mkyoung(pmd))));
pmd = pmd_mkold(pmd);
orig_pmd = pmd_mkold(orig_pmd);
pmde = pmd_mkold(pmde);
orig_pmd = pmd_mkold(orig_pmd);