From e346e6688c4aa18588f2c6a75b572d8ca7a65f5f Mon Sep 17 00:00:00 2001 From: Yang Shi Date: Wed, 30 Jun 2021 18:51:55 -0700 Subject: [PATCH] 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@gmail.com Signed-off-by: Yang Shi Acked-by: Mel Gorman Cc: Christian Borntraeger Cc: Gerald Schaefer Cc: Heiko Carstens Cc: Huang Ying Cc: Hugh Dickins Cc: Kirill A. Shutemov Cc: Michal Hocko Cc: Vasily Gorbik Cc: Zi Yan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/huge_memory.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index de7a8c2a0c80..dc0a0c82a5ac 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1742,6 +1742,7 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr, * 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_struct *vma, pmd_t *pmd, 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; -- 2.20.1