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

Shakeel Butt
2025-10-07T17:57:03Z

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

With that, please add:

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>