Re: [PATCH 2/2] mm/migrate: exclude hugetlb folios from MTHP_STAT_NR_ANON accounting

[Zi Yan]

On Thu Jul 2, 2026 at 1:25 PM EDT, Nico Pache wrote:
> __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 both places in
> __folio_migrate_mapping() so that only actual mTHP folios are counted.
>
> Fixes: 5d65c8d758f2 ("mm: count the number of anonymous THPs per size")
> Co-developed-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Nico Pache <npache@xxxxxxxxxx>
> ---
>  mm/migrate.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
LGTM. Thanks.

Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>

-- 
Best Regards,
Yan, Zi