[PATCH v2 1/2] mm: decrement MTHP_STAT_NR_ANON in free_zone_device_folio()

When a zone device folio is mapped as anonymous, folio_add_new_anon_rmap()
increments MTHP_STAT_NR_ANON. The corresponding decrement lives in
__free_pages_prepare() in page_alloc.c, but zone device folios are freed
via free_zone_device_folio() which never calls __free_pages_prepare().
This causes nr_anon to remain permanently elevated after zone device
folios are freed.

Add the missing mod_mthp_stat() decrement to free_zone_device_folio()
so that the counter is properly balanced.

Fixes: 5d65c8d758f2 ("mm: count the number of anonymous THPs per size")
Reviewed-by: Zi Yan <[email protected]>
Co-developed-by: David Hildenbrand <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
Signed-off-by: Nico Pache <[email protected]>
---
 mm/memremap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/memremap.c b/mm/memremap.c
index 81766d822400..accba23aef28 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -425,6 +425,7 @@ void free_zone_device_folio(struct folio *folio)
 	mem_cgroup_uncharge(folio);
 
 	if (folio_test_anon(folio)) {
+		mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, -1);
 		for (i = 0; i < nr; i++)
 			__ClearPageAnonExclusive(folio_page(folio, i));
 	}
-- 
2.55.0