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

David Hildenbrand
2021-12-07T15:09:54Z

On 07.12.21 14:23, Michal Hocko wrote:
> On Tue 07-12-21 13:28:31, David Hildenbrand wrote:
> [...]
>> But maybe I am missing something important regarding online vs. offline
>> nodes that your patch changes?
>
> I am relying on alloc_node_data setting the node online. But if we are
> to change the call to arch_alloc_node_data then the patch needs to be
> more involved. Here is what I have right now. If this happens to be the
> right way then there is some additional work to sync up with the hotplug
> code.
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c5952749ad40..a296e934ad2f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8032,8 +8032,23 @@ void __init free_area_init(unsigned long *max_zone_pfn)
> /* Initialise every node */
> mminit_verify_pageflags_layout();
> setup_nr_node_ids();
> - for_each_online_node(nid) {
> - pg_data_t *pgdat = NODE_DATA(nid);
> + for_each_node(nid) {
> + pg_data_t *pgdat;
> +
> + if (!node_online(nid)) {
> + pr_warn("Node %d uninitialized by the platform. Please report with memory map.\n", nid);
> + pgdat = arch_alloc_nodedata(nid);
> + pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat);
> + arch_refresh_nodedata(nid, pgdat);
> + node_set_online(nid);

Setting all possible nodes online might result in quite some QE noice,
because all these nodes will then be visible in the sysfs and
try_offline_nodes() is essentially for the trash.

I agree to prealloc the pgdat, I don't think we should actually set the
nodes online. Node onlining/offlining should be done when we do have
actual CPUs/memory populated.

--
Thanks,

David / dhildenb