Re: [PATCH v2 2/2] mm/memcg: migrate per-node hugetlb lruvec stat together with hugetlb folio

[Muchun Song <muchun.song@linux.dev>]

On 2026/9/23 10:05, Hongfu Li wrote:
> From: Hongfu Li <lihongfu@kylinos.cn>
>
> memory.numa_stat exposes per-node hugetlb counters from per-node lruvec
> stats. These stats are accounted against folio_nid(): incremented on
> the folio's node when handed to a user, decremented when the folio is
> returned to the pool.
>
> During hugetlb folio migration, mem_cgroup_migrate() moves the charge
> to the new folio and drops the memcg data of the old one, so the free
> of the old folio right after the migration skips the memcg per-node
> lruvec decrement. The hugetlb count stays attributed to the old node
> for the rest of the life of the charge, while the target folio gets no
> increment on the new node; its later free decrements a counter that
> was never incremented.
>
> Migrate the per-node lruvec accounting alongside migration. Global
> memcg totals remain balanced because they track resource consumption,
> not node placement.
>
> Fixes: 05d4532b60e3 ("memcg/hugetlb: add hugeTLB counters to memcg")
> Cc: stable@vger.kernel.org
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
> Tested-by: Joshua Hahn <joshua.hahnjy@gmail.com>
> Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> ---
>   include/linux/memcontrol.h |  8 ++++++++
>   mm/hugetlb.c               | 25 +++++++++++++++++++++++++
>   mm/memcontrol.c            |  5 ++---
>   3 files changed, 35 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index a8358f297b65..74110a324f9e 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -984,6 +984,9 @@ unsigned long lruvec_page_state_monotonic(const struct lruvec *lruvec,
>   unsigned long lruvec_page_state_local(const struct lruvec *lruvec,
>   				      enum node_stat_item idx);
>   
> +void mod_memcg_lruvec_state(struct lruvec *lruvec,
> +			    enum node_stat_item idx, int val);
> +
>   void mem_cgroup_flush_stats(struct mem_cgroup *memcg);
>   void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg);
>   
> @@ -1452,6 +1455,11 @@ static inline unsigned long lruvec_page_state_local(const struct lruvec *lruvec,
>   	return node_page_state(lruvec_pgdat(lruvec), idx);
>   }
>   
> +static inline void mod_memcg_lruvec_state(struct lruvec *lruvec,
> +					  enum node_stat_item idx, int val)
> +{
> +}
> +
>   static inline void mem_cgroup_flush_stats(struct mem_cgroup *memcg)
>   {
>   }
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 519c30b338a8..76d019594b39 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -23,6 +23,7 @@
>   #include <linux/mmdebug.h>
>   #include <linux/sched/signal.h>
>   #include <linux/rmap.h>
> +#include <linux/rcupdate.h>
>   #include <linux/string_choices.h>
>   #include <linux/string_helpers.h>
>   #include <linux/swap.h>
> @@ -7378,12 +7379,36 @@ void folio_putback_hugetlb(struct folio *folio)
>   	folio_put(folio);
>   }
>   
> +static void move_hugetlb_lruvec_stat(struct folio *old_folio,
> +				     struct folio *new_folio)
> +{
> +	struct mem_cgroup *memcg;
> +	long nr_pages = folio_nr_pages(old_folio);
> +	int old_nid = folio_nid(old_folio);
> +	int new_nid = folio_nid(new_folio);
> +
> +	if (old_nid == new_nid)
> +		return;
> +
> +	guard(rcu)();
> +
> +	memcg = folio_memcg(new_folio);
> +	if (!memcg)
> +		return;
> +
> +	mod_memcg_lruvec_state(mem_cgroup_lruvec(memcg, NODE_DATA(old_nid)),
> +			       NR_HUGETLB, -nr_pages);

Why not use mod_lruvec_state? mod_memcg_lruvec_state is an internal
API for memcg, I don't want it to be exported.

Thanks.

> +	mod_memcg_lruvec_state(mem_cgroup_lruvec(memcg, NODE_DATA(new_nid)),
> +			       NR_HUGETLB, nr_pages);
> +}
> +
>   void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio,
>   			enum migrate_reason reason)
>   {
>   	struct hstate *h = folio_hstate(old_folio);
>   
>   	hugetlb_cgroup_migrate(old_folio, new_folio);
> +	move_hugetlb_lruvec_stat(old_folio, new_folio);
>   	folio_set_owner_migrate_reason(new_folio, reason);
>   
>   	/*
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 88824f783571..a5335da5d425 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1015,9 +1015,8 @@ static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn,
>   	put_cpu();
>   }
>   
> -static void mod_memcg_lruvec_state(struct lruvec *lruvec,
> -				     enum node_stat_item idx,
> -				     int val)
> +void mod_memcg_lruvec_state(struct lruvec *lruvec,
> +			    enum node_stat_item idx, int val)
>   {
>   	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
>   	struct mem_cgroup_per_node *pn;
>