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

[Hongfu Li <hongfu.li@linux.dev>]

On 9/22/26 2:18 PM, Muchun Song wrote:
>
>> On Sep 21, 2026, at 17:12, Hongfu Li <hongfu.li@linux.dev> 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>
>> ---
>> mm/memcontrol.c | 31 +++++++++++++++++++++++++++++++
>> 1 file changed, 31 insertions(+)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 1460cba53588..9c96ebd5436f 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -5598,6 +5598,34 @@ void mem_cgroup_replace_folio(struct folio *old, struct folio *new)
>> rcu_read_unlock();
>> }
>>
>> +#ifdef CONFIG_HUGETLB_PAGE
>> +static void move_hugetlb_lruvec_stat(struct obj_cgroup *objcg,
> Actually, we don't need this objcg parameter since we could get it from folio.
> And I'd like to move this function to hugetlb.c.
>
>> +     				struct folio *old, struct folio *new)
>> +{
>> + 	long nr_pages = folio_nr_pages(old);
>> + 	struct mem_cgroup *memcg;
>> + 	int old_nid = folio_nid(old);
>> + 	int new_nid = folio_nid(new);
>> +
>> + 	if (old_nid == new_nid)
>> + 		return;
>> +
>> + 	rcu_read_lock();
> Please use guard(rcu)() to simplify the code a little.

Hi Muchun,

Thanks a lot for your suggestions. I will drop the objcg parameter of
move_hugetlb_lruvec_stat(), move the function to mm/hugetlb.c, and use
guard(rcu)() in it.  I will post a v2 for review shortly.

>> + 	memcg = obj_cgroup_memcg(objcg);
>> + 	mod_memcg_lruvec_state(mem_cgroup_lruvec(memcg, NODE_DATA(old_nid)),
>> +       		NR_HUGETLB, -nr_pages);
>> + 	mod_memcg_lruvec_state(mem_cgroup_lruvec(memcg, NODE_DATA(new_nid)),
>> +       		NR_HUGETLB, nr_pages);
>> + 	rcu_read_unlock();
>> +}
>> +#else /* CONFIG_HUGETLB_PAGE */
>> +static inline void move_hugetlb_lruvec_stat(struct obj_cgroup *objcg,
>> +    					struct folio *old,
>> +    					struct folio *new)
>> +{
>> +}
>> +#endif /* CONFIG_HUGETLB_PAGE */
>> +
>> /**
>>   * mem_cgroup_migrate - Transfer the memcg data from the old to the new folio.
>>   * @old: Currently circulating folio.
>> @@ -5635,6 +5663,9 @@ void mem_cgroup_migrate(struct folio *old, struct folio *new)
>>
>> 	new_objcg = get_migration_objcg(old, new);
>>
>> + 	if (folio_test_hugetlb(old))
>> + 		move_hugetlb_lruvec_stat(new_objcg, old, new);
>> +
>> /*
>> * @old was charged through a non-root objcg, so its charge is in the
>> * page counters. If the re-derivation walked up to the root objcg -
>>
>> -- 
>> 2.54.0
>>
-- 
Best regards,
Hongfu