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

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 <[email protected]>
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/[email protected]
Fixes: 5d65c8d758f2 ("mm: count the number of anonymous THPs per size")
Co-developed-by: David Hildenbrand <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
Signed-off-by: Nico Pache <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Rakie Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 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 [email protected] 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