Re: [PATCH v2] mm/memory_hotplug: maintain N_NORMAL_MEMORY during hotplug

Vlastimil Babka (SUSE)
2026-03-30T12:07:36Z

On 3/30/26 05:57, Hao Li wrote:
> N_NORMAL_MEMORY is initialized from zone population at boot, but memory
> hotplug currently only updates N_MEMORY. As a result, a node that gains
> normal memory via hotplug can remain invisible to users iterating over
> N_NORMAL_MEMORY, while a node that loses its last normal memory can stay
> incorrectly marked as such.
>
> Restore N_NORMAL_MEMORY maintenance directly in online_pages() and
> offline_pages(). Set the bit when a node that currently lacks normal
> memory onlines pages into a zone <= ZONE_NORMAL, and clear it when
> offlining removes the last present pages from zones <= ZONE_NORMAL.
>
> This restores the intended semantics without bringing back the old
> status_change_nid_normal notifier plumbing which was removed in
> 8d2882a8edb8.
>
> Current users that benefit include list_lru, zswap, nfsd filecache,
> hugetlb_cgroup, and has_normal_memory sysfs reporting.
>
> Fixes: 8d2882a8edb8 ("mm,memory_hotplug: remove status_change_nid_normal and update documentation")
> Signed-off-by: Hao Li <hao.li@linux.dev>

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Thanks!

> ---
> Changes: simplify the code. (Thanks Joshua and David)
> ---
> mm/memory_hotplug.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index bc805029da51..05a47953ef21 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1209,6 +1209,13 @@ int online_pages(unsigned long pfn, unsigned long nr_pages,
>
> if (node_arg.nid >= 0)
> node_set_state(nid, N_MEMORY);
> + /*
> + * Check whether we are adding normal memory to the node for the first
> + * time.
> + */
> + if (!node_state(nid, N_NORMAL_MEMORY) && zone_idx(zone) <= ZONE_NORMAL)
> + node_set_state(nid, N_NORMAL_MEMORY);
> +
> if (need_zonelists_rebuild)
> build_all_zonelists(NULL);
>
> @@ -1908,6 +1915,8 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages,
> unsigned long flags;
> char *reason;
> int ret;
> + unsigned long normal_pages = 0;
> + enum zone_type zt;
>
> /*
> * {on,off}lining is constrained to full memory sections (or more
> @@ -2055,6 +2064,17 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages,
> /* reinitialise watermarks and update pcp limits */
> init_per_zone_wmark_min();
>
> + /*
> + * Check whether this operation removes the last normal memory from
> + * the node. We do this before clearing N_MEMORY to avoid the possible
> + * transient "!N_MEMORY && N_NORMAL_MEMORY" state.
> + */
> + if (zone_idx(zone) <= ZONE_NORMAL) {
> + for (zt = 0; zt <= ZONE_NORMAL; zt++)
> + normal_pages += pgdat->node_zones[zt].present_pages;
> + if (!normal_pages)
> + node_clear_state(node, N_NORMAL_MEMORY);
> + }
> /*
> * Make sure to mark the node as memory-less before rebuilding the zone
> * list. Otherwise this node would still appear in the fallback lists.