mm: Move change_prot_numa outside CONFIG_ARCH_USES_NUMA_PROT_NONE

change_prot_numa should work even if _PAGE_NUMA != _PAGE_PROTNONE.
On archs like ppc64 that don't use _PAGE_PROTNONE and also have
a separate page table outside linux pagetable, we just need to
make sure that when calling change_prot_numa we flush the
hardware page table entry so that next page access result in a numa
fault.

We still need to make sure we use the numa faulting logic only
when CONFIG_NUMA_BALANCING is set. This implies the migrate-on-fault
(Lazy migration) via mbind will only work if CONFIG_NUMA_BALANCING
is set.

Signed-off-by: Aneesh Kumar K.V <[e-mail]>
Reviewed-by: Rik van Riel <[e-mail]>
Acked-by: Mel Gorman <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

include/linux/mm.h

···
 }
 #endif
 
-#ifdef CONFIG_ARCH_USES_NUMA_PROT_NONE
+#ifdef CONFIG_NUMA_BALANCING
 unsigned long change_prot_numa(struct vm_area_struct *vma,
 			unsigned long start, unsigned long end);
 #endif

mm/mempolicy.c

···
 	return 0;
 }
 
-#ifdef CONFIG_ARCH_USES_NUMA_PROT_NONE
+#ifdef CONFIG_NUMA_BALANCING
 /*
  * This is used to mark a range of virtual addresses to be inaccessible.
  * These are later cleared by a NUMA hinting fault. Depending on these
···
 			unsigned long addr, unsigned long end)
 {
 	int nr_updated;
-	BUILD_BUG_ON(_PAGE_NUMA != _PAGE_PROTNONE);
 
 	nr_updated = change_protection(vma, addr, end, vma->vm_page_prot, 0, 1);
 	if (nr_updated)
···
 {
 	return 0;
 }
-#endif /* CONFIG_ARCH_USES_NUMA_PROT_NONE */
+#endif /* CONFIG_NUMA_BALANCING */
 
 /*
  * Walk through page tables and collect pages to be migrated.