mm/migrate: exclude hugetlb folios from MTHP_STAT_NR_ANON accounting

__folio_migrate_mapping() increments MTHP_STAT_NR_ANON for the destination
folio when `folio_test_anon(folio) && folio_test_large(folio)` is true.
However, hugetlb folios satisfy both conditions despite having a
completely separate accounting system — they use hugetlb_add_anon_rmap()
which does not touch mTHP stats, and their free path also bypasses the
mTHP decrement in __free_pages_prepare().

This causes MTHP_STAT_NR_ANON to be incremented on each hugetlb migration
without a corresponding decrement, permanently inflating the nr_anon
counter.

Add a !folio_test_hugetlb() check to __folio_migrate_mapping() so that
only actual mTHP folios are counted.

Link: https://lore.kernel.org/20260717064502.1980173-3-npache@redhat.com
Fixes: 5d65c8d758f2 ("mm: count the number of anonymous THPs per size")
Co-developed-by: David Hildenbrand <david@kernel.org>
Signed-off-by: David Hildenbrand <david@kernel.org>
Signed-off-by: Nico Pache <npache@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rakie Kim <rakie.kim@sk.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index d9b23909d716c6b5e94e3266c39083f70a7e050f..dd15a84b2a52aee329e40982395a3a215b3088bd 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -590,7 +590,8 @@ static int __folio_migrate_mapping(struct address_space *mapping,
                /* No turning back from here */
                newfolio->index = folio->index;
                newfolio->mapping = folio->mapping;
-               if (folio_test_anon(folio) && folio_test_large(folio))
+               if (folio_test_anon(folio) && folio_test_large(folio) &&
+                   !folio_test_hugetlb(folio))
                        mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, 1);
                if (folio_test_swapbacked(folio))
                        __folio_set_swapbacked(newfolio);