[patch 032/119] mm, page_alloc: do not set_cpu_numa_mem on empty nodes initialization

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From: Michal Hocko <mhocko@xxxxxxxx>
Subject: 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/20170721143915.14161-4-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Joonsoo Kim <js1304@xxxxxxxxx>
Cc: Shaohua Li <shaohua.li@xxxxxxxxx>
Cc: Toshi Kani <toshi.kani@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/page_alloc.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff -puN mm/page_alloc.c~mm-page_alloc-do-not-set_cpu_numa_mem-on-empty-nodes-initialization mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_alloc-do-not-set_cpu_numa_mem-on-empty-nodes-initialization
+++ a/mm/page_alloc.c
@@ -5160,10 +5160,8 @@ static int __build_all_zonelists(void *d
 
 			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 *d
 		 * 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;
 }
_
--
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