Re: [Patch 2/2]: powerpc/hotplug/mm: Fix hot-add memory node assoc

From: Reza Arbab
Date: Tue May 23 2017 - 17:49:37 EST


On Tue, May 23, 2017 at 03:05:08PM -0500, Michael Bringmann wrote:
On 05/23/2017 10:52 AM, Reza Arbab wrote:
On Tue, May 23, 2017 at 10:15:44AM -0500, Michael Bringmann wrote:
+static void setup_nodes(void)
+{
+ int i, l = 32 /* MAX_NUMNODES */;
+
+ for (i = 0; i < l; i++) {
+ if (!node_possible(i)) {
+ setup_node_data(i, 0, 0);
+ node_set(i, node_possible_map);
+ }
+ }
+}

This seems to be a workaround for 3af229f2071f ("powerpc/numa: Reset node_possible_map to only node_online_map").

They may be related, but that commit is not a replacement. The above patch ensures that
there are enough of the nodes initialized at startup to allow for memory hot-add into a
node that was not used at boot. (See 'setup_node_data' function in 'numa.c'.) That and
recording that the node was initialized.

Is it really necessary to preinitialize these empty nodes using setup_node_data()? When you do memory hotadd into a node that was not used at boot, the node data already gets set up by

add_memory
add_memory_resource
hotadd_new_pgdat
arch_alloc_nodedata <-- allocs the pg_data_t
...
free_area_init_node <-- sets NODE_DATA(nid)->node_id, etc.

Removing setup_node_data() from that loop leaves only the call to node_set(). If 3af229f2071f (which reduces node_possible_map) was reverted, you wouldn't need to do that either.

I didn't see where any part of commit 3af229f2071f would touch the 'node_possible_map'
which is needed by 'numa.c' and 'workqueue.c'. The nodemask created and updated by
'mem_cgroup_may_update_nodemask()' does not appear to be the same mask.

Are you sure you're looking at 3af229f2071f? It only adds one line of code; the reduction of node_possible_map.

--
Reza Arbab