linux-kernel - [PATCH 3/9] mm, page_alloc: do not set_cpu_numa

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Date:   Fri, 21 Jul 2017 16:39:09 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mel Gorman <mgorman@...e.de>, Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>, <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: [PATCH 3/9] mm, page_alloc: do not set_cpu_numa_mem on empty nodes initialization

From: Michal Hocko <mhocko@...e.com>

__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.

Acked-by: Mel Gorman <mgorman@...e.de>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/page_alloc.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ff53f709c44c..52dc5ba40914 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5096,10 +5096,8 @@ 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.
@@ -5108,10 +5106,10 @@ 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;
 }
-- 
2.11.0