+ mm-migrate-exclude-hugetlb-folios-from-mthp_stat_nr_anon-accounting.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: mm/migrate: exclude hugetlb folios from MTHP_STAT_NR_ANON accounting
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-migrate-exclude-hugetlb-folios-from-mthp_stat_nr_anon-accounting.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-exclude-hugetlb-folios-from-mthp_stat_nr_anon-accounting.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Nico Pache <npache@redhat.com>
Subject: mm/migrate: exclude hugetlb folios from MTHP_STAT_NR_ANON accounting
Date: Fri, 17 Jul 2026 00:45:00 -0600

__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>
---

 mm/migrate.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/migrate.c~mm-migrate-exclude-hugetlb-folios-from-mthp_stat_nr_anon-accounting
+++ a/mm/migrate.c
@@ -590,7 +590,8 @@ static int __folio_migrate_mapping(struc
 		/* 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);
_

Patches currently in -mm which might be from npache@redhat.com are

mm-decrement-mthp_stat_nr_anon-in-free_zone_device_folio.patch
mm-migrate-exclude-hugetlb-folios-from-mthp_stat_nr_anon-accounting.patch