On Thu, Jun 11, 2026 at 10:39 AM Lorenzo Stoakes <[email protected]> wrote:
>
> On Thu, Jun 11, 2026 at 09:58:55AM -0600, 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
>
> You're not giving any details? how does this manifest? How did you detect?
> Output? Etc.
When running my mTHP tests, I always have a terminal with
watch grep . /sys/kernel/mm/transparent_hugepage/hugepages-*/stats/nr_anon
I noticed that when I ran selftests the 2MB count remained elevated
even after the tests finished and the system memory was returned.
e.g)
/sys/kernel/mm/transparent_hugepage/hugepages-2048kB/stats/nr_anon:34831
>
> >
> > 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.
>
> Seems to be a regression in your editor's line wrapping... ;)
Haha yeah still figuring that one out :) The guide on setting up
Thunderbird recommends wrapping at 0 which seems wrong...
Hopefully I have it working correctly now.
>
> >
> > This issue occurs in two mm selftests:
> > 1) hmm test
> > 2) migration - private_anon_htlb test
>
> OK that's useful, but what exactly happened? Any test output?
Tests seem to be ok (although the HMM tests fails, but that's not new)
>
> >
> > I spoke to David about this and he suggested the following diff which seems
> > to have solved both issues.
>
> Whilst speaking to people off-list/elsewhere etc. is totally fine, I'd suggest
> engaging with the community as the first course of action is often a good way
> of
> resolving things.
>
> Even if things arise from private discussions, which is also totally fine,
> please do give sufficient context so that the community can engage with it.
That was my goal here :) Perhaps I fell short...
>
> And I would suggest that ideally you phrase things such that you are asking
> the
> community as a whole :)
>
> >
> > David would you like to send a formal patch or patches?
>
> So on that point, I understand you're asking David specifically because he
> suggested the patch, but I feel that you'd get better results making it clear
> that you want community input :)
Yeah I didn't want to just send a fix that wasn't authored by me, and
I didn't fully understand it. When I brought this up to David (during
a separate off-list conversation), he suggested fixes within minutes,
and asked me to test. This was the formal follow up.
>
> As one might misread this, and perhaps other such occasions, as you feeling
> THP
> == 1 person, which I am absolutely sure is not how you feel, but phrasing
> things
> a little differently would help underline that :)
>
> Kernel review and maintainership can be rather a thankless task, so details
> like
> this matter I feel! [and I realise I probably screw up on this regularly too
> so
> we're all constantly learning :)]
Yep! Still learning (and often failing :))
Cheers,
-- Nico
>
> >
> > Cheers,
> > -- Nico
>
> Thanks, Lorenzo
>
> >
> > 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));
> > }
> > --
> > 2.54.0
> >
> > For (2) he suggested
> >
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index d9b23909d716..9fd50ea25d2d 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))
> > --
> > 2.54.0
> >
>
