Re: [PATCH 0/2] mm/hugetlb_cgroup: move the per-node usage along with the folio

[Hongfu Li]

On 9/17/26 8:53 AM, Andrew Morton wrote:
> On Wed, 16 Sep 2026 16:30:26 +0800 Hongfu Li <hongfu.li@xxxxxxxxx> wrote:
>
> > The per-node usage reported by hugetlb.<size>.numa_stat is accounted
> > against folio_nid() in __hugetlb_cgroup_commit_charge() and
> > __hugetlb_cgroup_uncharge_folio(), so it is only correct while a folio
> > stays charged on the same node and in the same hugetlb_cgroup.
> >
> > Two paths move a folio which stays charged, and neither moves the usage
> > with it. hugetlb_cgroup_migrate() only moves the hugetlb_cgroup pointers
> > of a folio migrated to another node, and hugetlb_cgroup_move_parent()
> > only moves the page_counter charges and the hugetlb_cgroup pointer of
> > the folios of a dying cgroup. In both cases the node (or cgroup) which
> > was charged keeps a usage which never goes away, while the node
> > (or cgroup) which ends up uncharging the folio underflows as soon as
> > the folio is freed.
> >
> > Patch 1/2 moves the usage along with the folio on cross node migration,
> > patch 2/2 does the same for the folios a dying cgroup reparents.
> As I understand it, this series affects numa_stat output but has no
> actual runtime effects?

Yes, that's right. The per-node usage[] is only read by
hugetlb_cgroup_read_numa_stat(), so this series only fixes the values
reported in hugetlb.<size>.numa_stat. It has no effect on charging or
limit enforcement, which go through page_counter and are already
handled correctly by hugetlb_cgroup_migrate() and
hugetlb_cgroup_move_parent().

> Do you (and maintainers) think that we should fix this in earlier
> kernels?
>
> (I do - a lot of userspace infrastructure makes expensive decisions
> based on this sort of info).

I agree with you that this should go to stable.

Patch 1/2 and Patch 2/2 already carry Fixes: and Cc: stable tags.

--
Best regards,
Hongfu