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SubjectRe: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY
On Fri, Feb 16, 2024 at 04:07:54PM +0900, Byungchul Park wrote:
> For normal numa nodes, node_data[] is initialized at alloc_node_data(),
> but it's not for memoryless node. However, the node *gets onlined* at
> init_cpu_to_node().
>
> Let's look at back free_area_init(). free_area_init_node() will be called
> with node_data[] not set yet, because it's already *onlined*. So
> ->zone_pgdat cannot be initialized properly in the path you mentioned.

I am might be missing something., so bear with me.

free_area_init() gets called before init_cpu_to_node() does.
free_area_init_node() gets called on every possible node.

free_area_init_node then() does

pg_data_t *pgdat = NODE_DATA(nid);,

and then we call free_area_init_core().

free_area_init_core() does

free_area_init_core() does
zone_init_internals()

which ends up doing zone->zone_pgdat = NODE_DATA(nid);

If node_data[] was not set at all, we would already blow up when doing
the first

for_each_node()
pgdat = NODE_DATA(nid);
free_area_init_node(nid);

back in free_area_init().


--
Oscar Salvador
SUSE Labs

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