Re: [Bug Report] Elevated PMD nr_anon after running selftests

["David Hildenbrand (Arm)" <david@kernel.org>]

On 6/11/26 17:58, Nico Pache wrote:
> Hi,
> 
> While testing my mTHP code I noticed that mm selftests caused an accounting error in
> /sys/kernel/mm/transparent_hugepage/hugepages-2048kB/stats/nr_anon
> 
> At first I thought I might have caused a regression, but when retesting with 7.1-rc5 (without my code), the issue was still present.
> 
> This issue occurs in two mm selftests:
> 1) hmm test
> 2) migration - private_anon_htlb test
> 
> I spoke to David about this and he suggested the following diff which seems to have solved both issues.
> 
> David would you like to send a formal patch or patches?
> 
> Cheers,
> -- Nico
> 
> Diff for (1)
> 
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 053842d45cb1..683a77dd679d 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));
>         }

Wasn't there another issue with hugetlb?

diff --git a/mm/migrate.c b/mm/migrate.c
index 8a64291ab5b4..0aec894266f2 100644
--- 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);
@@ -623,7 +624,8 @@ static int __folio_migrate_mapping(struct address_space
*mapping,
         */
        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);
        folio_ref_add(newfolio, nr); /* add cache reference */
        if (folio_test_swapbacked(folio))


Yeah, if you have some capacity, please send patches (and figure out Fixes:) :)


-- 
Cheers,

David