Re: [PATCH v3] mm: fix panic in __alloc_pages

Michal Hocko
2021-12-08T08:04:27Z

On Tue 07-12-21 17:17:27, Alexey Makhalov wrote:
>
>
> > On Dec 7, 2021, at 9:13 AM, David Hildenbrand <david@redhat.com> wrote:
> >
> > On 07.12.21 18:02, Alexey Makhalov wrote:
> >>
> >>
> >>> 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.
> >
> > I already raised that PPC might be problematic in that regard. Which
> > architecture / setup do you have in mind that can have a lot of possible
> > nodes?
> >
> It is x86_64 VMware VM, not the regular one, but specially configured (1 vCPU per node,
> with hot-plug support, 128 possible nodes)

This is slightly tangent but could you elaborate more on this setup and
reasoning behind it. I was already curious when you mentioned this
previously. Why would you want to have so many nodes and having 1:1 with
CPUs. What is the resulting NUMA topology?
--
Michal Hocko
SUSE Labs