> On Dec 7, 2021, at 8:36 AM, Michal Hocko <mhocko@suse.com> wrote:
> 
> On Tue 07-12-21 17:27:29, Michal Hocko wrote:
> [...]
>> So your proposal is to drop set_node_online from the patch and add it as
>> a separate one which handles
>> 	- sysfs part (i.e. do not register a node which doesn't span a
>> 	  physical address space)
>> 	- hotplug side of (drop the pgd allocation, register node lazily
>> 	  when a first memblocks are registered)
> 
> In other words, the first stage
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c5952749ad40..f9024ba09c53 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6382,7 +6382,11 @@ static void __build_all_zonelists(void *data)
> 	if (self && !node_online(self->node_id)) {
> 		build_zonelists(self);
> 	} else {
> -		for_each_online_node(nid) {
> +		/*
> +		 * All possible nodes have pgdat preallocated
> +		 * free_area_init
> +		 */
> +		for_each_node(nid) {
> 			pg_data_t *pgdat = NODE_DATA(nid);
> 
> 			build_zonelists(pgdat);

Will it blow up memory usage for the nodes which might never be onlined?
I prefer the idea of init on demand.

Even now there is an existing problem.
In my experiments, I observed _huge_ memory consumption increase by increasing number
of possible numa nodes. I’m going to report it in separate mail thread.

Thanks,
—-Alexey