Re: [RFC PATCH 2/6] mm: memcg: make memcg huge page split support any order split.

[Roman Gushchin]

On Wed, Nov 11, 2020 at 03:40:04PM -0500, Zi Yan wrote:
> From: Zi Yan <ziy@xxxxxxxxxx>
> 
> It reads thp_nr_pages and splits to provided new_nr. It prepares for
> upcoming changes to support split huge page to any lower order.
> 
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
>  include/linux/memcontrol.h | 5 +++--
>  mm/huge_memory.c           | 2 +-
>  mm/memcontrol.c            | 4 ++--
>  3 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 0f4dd7829fb2..b3bac79ceed6 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1105,7 +1105,7 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
>  }
>  
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -void mem_cgroup_split_huge_fixup(struct page *head);
> +void mem_cgroup_split_huge_fixup(struct page *head, unsigned int new_nr);
>  #endif
>  
>  #else /* CONFIG_MEMCG */
> @@ -1451,7 +1451,8 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
>  	return 0;
>  }
>  
> -static inline void mem_cgroup_split_huge_fixup(struct page *head)
> +static inline void mem_cgroup_split_huge_fixup(struct page *head,
> +					       unsigned int new_nr)
>  {
>  }
>  
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index c4fead5ead31..f599f5b9bf7f 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2429,7 +2429,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>  	lruvec = mem_cgroup_page_lruvec(head, pgdat);
>  
>  	/* complete memcg works before add pages to LRU */
> -	mem_cgroup_split_huge_fixup(head);
> +	mem_cgroup_split_huge_fixup(head, 1);
>  
>  	if (PageAnon(head) && PageSwapCache(head)) {
>  		swp_entry_t entry = { .val = page_private(head) };
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 33f632689cee..e9705ba6bbcc 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3247,7 +3247,7 @@ void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size)
>   * Because tail pages are not marked as "used", set it. We're under
>   * pgdat->lru_lock and migration entries setup in all page mappings.
>   */
> -void mem_cgroup_split_huge_fixup(struct page *head)
> +void mem_cgroup_split_huge_fixup(struct page *head, unsigned int new_nr)

I'd go with unsigned int new_order, then it's obvious that we can split
the original page without any leftovers.

Other than that the patch looks good!
Acked-by: Roman Gushchin <guro@xxxxxx>

Thanks!

>  {
>  	struct mem_cgroup *memcg = page_memcg(head);
>  	int i;
> @@ -3255,7 +3255,7 @@ void mem_cgroup_split_huge_fixup(struct page *head)
>  	if (mem_cgroup_disabled())
>  		return;
>  
> -	for (i = 1; i < thp_nr_pages(head); i++) {
> +	for (i = new_nr; i < thp_nr_pages(head); i += new_nr) {
>  		css_get(&memcg->css);
>  		head[i].memcg_data = (unsigned long)memcg;
>  	}
> -- 
> 2.28.0
>