[089/192] mm: thp: skip make PMD PROT_NONE if THP migration is not supported

Commit Message

Andrew Morton July 1, 2021, 1:51 a.m. UTC

From: Yang Shi <[e-mail]>
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/[e-mail]
Signed-off-by: Yang Shi <[e-mail]>
Acked-by: Mel Gorman <[e-mail]>
Cc: Christian Borntraeger <[e-mail]>
Cc: Gerald Schaefer <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Huang Ying <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Cc: Zi Yan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/huge_memory.c |    4 ++++
 1 file changed, 4 insertions(+)

Patch

--- 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;