Re: [PATCH v2 2/2] mm: memory_hotplug: drop memoryless node from fallback lists

[David Hildenbrand]

On 19.10.23 09:36, Qi Zheng wrote:
> In offline_pages(), if a node becomes memoryless, we
> will clear its N_MEMORY state by calling node_states_clear_node().
> But we do this after rebuilding the zonelists by calling
> build_all_zonelists(), which will cause this memoryless node to
> still be in the fallback list of other nodes. This will incur
> some runtime overhead.
>
> To drop memoryless node from fallback lists in this case, just
> call node_states_clear_node() before calling build_all_zonelists().
>
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> ---
>   mm/memory_hotplug.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index d4a364fdaf8f..18af399627f0 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -2036,12 +2036,12 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>   	/* reinitialise watermarks and update pcp limits */
>   	init_per_zone_wmark_min();
>   
> +	node_states_clear_node(node, &arg);
>   	if (!populated_zone(zone)) {
>   		zone_pcp_reset(zone);
>   		build_all_zonelists(NULL);
>   	}
>   
> -	node_states_clear_node(node, &arg);
>   	if (arg.status_change_nid >= 0) {
>   		kcompactd_stop(node);
>   		kswapd_stop(node);

Probably worth a comment.

/*
 * Make sure to mark the node as memory-less before rebuilding the zone
 * list. Otherwise this node would still appear in the fallback lists.
 */

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers,

David / dhildenb