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>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9327a940e373a5945f297c3853ebc46a57990420..dcc8a1cf55b606ac8da70243125b496f9f81e178 100644 (file)
--- 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);
+               }
        }
 
        /*