Commit e346e668 authored by Yang Shi's avatar Yang Shi Committed by Linus Torvalds
Browse files

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: default avatarYang Shi <shy828301@gmail.com>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 662aeea7

mm/huge_memory.c

+4 −0
Original line number Diff line number Diff line
@@ -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;