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

Hao Li
2026-03-30T04:00:26Z

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>
---
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.
--
2.50.1