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

[Andrew Morton]

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?

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).