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[v2,7/7] mm: thp: skip make PMD PROT_NONE if THP migration is not supported

Message ID 20210413212416.3273-8-shy828301@gmail.com (mailing list archive)
State New
Headers show
Series mm: thp: use generic THP migration for NUMA hinting fault | expand

Commit Message

Yang Shi April 13, 2021, 9:24 p.m. UTC
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.

Signed-off-by: Yang Shi <shy828301@gmail.com>
 mm/huge_memory.c | 4 ++++
 1 file changed, 4 insertions(+)
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diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 94981907fd4c..f63445f3a17d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1741,6 +1741,7 @@  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,
@@ -1755,6 +1756,9 @@  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;