Re: [PATCH v2 1/2] mm/hugetlb_cgroup: move per-node usage on cross node migration

[Muchun Song]

> On Sep 18, 2026, at 10:56, Hongfu Li <hongfu.li@xxxxxxxxx> wrote:
> 
> From: Hongfu Li <lihongfu@xxxxxxxxxx>
> 
> hugetlb.<size>.numa_stat uses folio_nid() to account usage in
> __hugetlb_cgroup_commit_charge() and __hugetlb_cgroup_uncharge_folio().
> hugetlb_cgroup_migrate() only moves hugetlb_cgroup pointers, leaving
> per-node usage behind on the source node during cross-node migration.
> 
> When the migrated folio gets uncharged, we subtract usage from the
> destination node counter. This creates stale usage on the source node
> and unsigned long counter underflow on the destination node.
> The hugetlb.<size>.numa_stat interface exposes these incorrect per-node
> usage values to userspace.
> 
> Add a hugetlb_cgroup_move_usage() helper which moves the usage from the
> old node to the new node, and call it from hugetlb_cgroup_migrate().
> 
> Fixes: f47761999052 ("hugetlb: add hugetlb.*.numa_stat file")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Hongfu Li <lihongfu@xxxxxxxxxx>

Acked-by: Muchun Song <muchun.song@xxxxxxxxx>

Thanks.