Re: [PATCH v4 4/4] mm: thp: reparent the split queue during memcg offline

Qi Zheng
2025-10-13T07:29:38Z

Hi Shakeel,

On 10/8/25 1:56 AM, Shakeel Butt wrote:
> On Sat, Oct 04, 2025 at 12:53:18AM +0800, Qi Zheng wrote:
>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>
>> Similar to list_lru, the split queue is relatively independent and does
>> not need to be reparented along with objcg and LRU folios (holding
>> objcg lock and lru lock). So let's apply the similar mechanism as list_lru
>> to reparent the split queue separately when memcg is offine.
>>
>> This is also a preparation for reparenting LRU folios.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>> include/linux/huge_mm.h | 4 +++
>> mm/huge_memory.c | 54 +++++++++++++++++++++++++++++++++++++++++
>> mm/memcontrol.c | 1 +
>> 3 files changed, 59 insertions(+)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index f327d62fc9852..0c211dcbb0ec1 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -417,6 +417,9 @@ static inline int split_huge_page(struct page *page)
>> return split_huge_page_to_list_to_order(page, NULL, ret);
>> }
>> void deferred_split_folio(struct folio *folio, bool partially_mapped);
>> +#ifdef CONFIG_MEMCG
>> +void reparent_deferred_split_queue(struct mem_cgroup *memcg);
>> +#endif
>>
>> void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>> unsigned long address, bool freeze);
>> @@ -611,6 +614,7 @@ static inline int try_folio_split(struct folio *folio, struct page *page,
>> }
>>
>> static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {}
>> +static inline void reparent_deferred_split_queue(struct mem_cgroup *memcg) {}
>> #define split_huge_pmd(__vma, __pmd, __address) \
>> do { } while (0)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 59ddebc9f3232..b5eea2091cdf6 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -1099,6 +1099,11 @@ static struct deferred_split *memcg_split_queue(int nid, struct mem_cgroup *memc
>> {
>> return memcg ? &memcg->deferred_split_queue : split_queue_node(nid);
>> }
>> +
>> +static bool memcg_is_dying(struct mem_cgroup *memcg)
>> +{
>> + return memcg ? css_is_dying(&memcg->css) : false;
>> +}
>
> Please move the above function to include/linux/memcontrol.h

OK, will do.

>
> With that, please add:
>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>

Thanks!

>