mm: access zone->node via zone_to_nid() and zone_set_nid()

zone->node is configured only when CONFIG_NUMA=y, so it is a good idea to
have inline functions to access this field in order to avoid ifdef's in c
files.

Link: http://lkml.kernel.org/r/20180730101757.28058-3-osalvador@techadventures.net
Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Aaron Lu <aaron.lu@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Pasha Tatashin <Pavel.Tatashin@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 5b72266..6838a53 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -53,13 +53,8 @@ void __init mminit_verify_zonelist(void)
 				zone->name);
 
 			/* Iterate the zonelist */
-			for_each_zone_zonelist(zone, z, zonelist, zoneid) {
-#ifdef CONFIG_NUMA
-				pr_cont("%d:%s ", zone->node, zone->name);
-#else
-				pr_cont("0:%s ", zone->name);
-#endif /* CONFIG_NUMA */
-			}
+			for_each_zone_zonelist(zone, z, zonelist, zoneid)
+				pr_cont("%d:%s ", zone_to_nid(zone), zone->name);
 			pr_cont("\n");
 		}
 	}