From: Yang Shi <shy828301@xxxxxxxxx> Subject: mm: thp: skip make PMD PROT_NONE if THP migration is not supported A quick grep shows x86_64, PowerPC (book3s), ARM64 and S390 support both NUMA balancing and THP. But S390 doesn't support THP migration so NUMA balancing actually can't migrate any misplaced pages. Skip make PMD PROT_NONE for such case otherwise CPU cycles may be wasted by pointless NUMA hinting faults on S390. Link: https://lkml.kernel.org/r/20210518200801.7413-8-shy828301@xxxxxxxxx Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxx> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> Cc: Heiko Carstens <hca@xxxxxxxxxxxxx> Cc: Huang Ying <ying.huang@xxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/mm/huge_memory.c~mm-thp-skip-make-pmd-prot_none-if-thp-migration-is-not-supported +++ a/mm/huge_memory.c @@ -1742,6 +1742,7 @@ bool move_huge_pmd(struct vm_area_struct * Returns * - 0 if PMD could not be locked * - 1 if PMD was locked but protections unchanged and TLB flush unnecessary + * or if prot_numa but THP migration is not supported * - HPAGE_PMD_NR if protections changed and TLB flush necessary */ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, @@ -1756,6 +1757,9 @@ int change_huge_pmd(struct vm_area_struc bool uffd_wp = cp_flags & MM_CP_UFFD_WP; bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; + if (prot_numa && !thp_migration_supported()) + return 1; + ptl = __pmd_trans_huge_lock(pmd, vma); if (!ptl) return 0; _
