mm/memory_hotplug: just build zonelist for newly added node

Commit 9adb62a5df9c ("mm/hotplug: correctly setup fallback zonelists
when creating new pgdat") tries to build the correct zonelist for a
newly added node, while it is not necessary to rebuild it for already
exist nodes.

In build_zonelists(), it will iterate on nodes with memory.  For a newly
added node, it will have memory until node_states_set_node() is called
in online_pages().

This patch avoids rebuilding the zonelists for already existing nodes.

build_zonelists_node() uses managed_zone(zone) checks, so it should not
include empty zones anyway.  So effectively we avoid some pointless work
under stop_machine().

[akpm@linux-foundation.org: tweak comment text]
[akpm@linux-foundation.org: coding-style tweak, per Vlastimil]
Link: http://lkml.kernel.org/r/20170626035822.50155-1-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jiang Liu <liuj97@gmail.com>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 5 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9327a940e373..dcc8a1cf55b6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5282,14 +5282,18 @@ static int __build_all_zonelists(void *data)
         memset(node_load, 0, sizeof(node_load));
 #endif
 
+        /*
+         * This node is hotadded and no memory is yet present.   So just
+         * building zonelists is fine - no need to touch other nodes.
+         */
         if (self && !node_online(self->node_id)) {
                 build_zonelists(self);
-        }
-
-        for_each_online_node(nid) {
-                pg_data_t *pgdat = NODE_DATA(nid);
+        } else {
+                for_each_online_node(nid) {
+                        pg_data_t *pgdat = NODE_DATA(nid);
 
-                build_zonelists(pgdat);
+                        build_zonelists(pgdat);
+                }
         }
 
         /*