Commit 2ecbe06a authored by Hao Li's avatar Hao Li Committed by Andrew Morton
Browse files

mm/memory_hotplug: maintain N_NORMAL_MEMORY during hotplug 

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.

The most visible effect is that
/sys/devices/system/node/has_normal_memory does not report a node even
after that node has gained normal memory via hotplug.

Also, list_lru-based shrinkers can undercount objects on such a node
and may skip reclaim on that node entirely, which can lead to a higher
memory footprint than expected.

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
8d2882a8.

Current users that benefit include list_lru, zswap, nfsd filecache,
hugetlb_cgroup, and has_normal_memory sysfs reporting.

Link: https://lkml.kernel.org/r/20260330035941.518186-1-hao.li@linux.dev


Fixes: 8d2882a8 ("mm,memory_hotplug: remove status_change_nid_normal and update documentation")
Signed-off-by: default avatarHao Li <hao.li@linux.dev>
Reviewed-by: default avatarHarry Yoo (Oracle) <harry@kernel.org>
Acked-by: default avatarVlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: default avatarJoshua Hahn <joshua.hahnjy@gmail.com>
Acked-by: default avatarDavid Hildenbrand (Arm) <david@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 0199390a

mm/memory_hotplug.c

+20 −0
Original line number Diff line number Diff line
@@ -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.