mm, page_alloc: do not set_cpu_numa_mem on empty nodes initialization

__build_all_zonelists reinitializes each online cpu local node for
CONFIG_HAVE_MEMORYLESS_NODES.  This makes sense because previously
memory less nodes could gain some memory during memory hotplug and so
the local node should be changed for CPUs close to such a node.  It
makes less sense to do that unconditionally for a newly creaded NUMA
node which is still offline and without any memory.

Let's also simplify the cpu loop and use for_each_online_cpu instead of
an explicit cpu_online check for all possible cpus.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Michal Hocko <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Toshi Kani <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/page_alloc.c

@@ -5160,10 +5160,8 @@ static int __build_all_zonelists(void *data)
 
 			build_zonelists(pgdat);
 		}
-	}
 
 #ifdef CONFIG_HAVE_MEMORYLESS_NODES
-	for_each_possible_cpu(cpu) {
 		/*
 		 * We now know the "local memory node" for each node--
 		 * i.e., the node of the first zone in the generic zonelist.
@@ -5172,10 +5170,10 @@ static int __build_all_zonelists(void *data)
 		 * secondary cpus' numa_mem as they come on-line.  During
 		 * node/memory hotplug, we'll fixup all on-line cpus.
 		 */
-		if (cpu_online(cpu))
+		for_each_online_cpu(cpu)
 			set_cpu_numa_mem(cpu, local_memory_node(cpu_to_node(cpu)));
-	}
 #endif
+	}
 
 	return 0;
 }