Re: [PATCH 3/5] mm: Remove references to folio in split_page_memcg()

[Johannes Weiner <hannes@cmpxchg.org>]

On Thu, Mar 13, 2025 at 02:58:52PM +0000, Matthew Wilcox (Oracle) wrote:
> @@ -2697,6 +2697,23 @@ static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
>  	return ret;
>  }
>  
> +static struct obj_cgroup *page_objcg(const struct page *first)

"first" is odd for that function. "page"?

> @@ -3091,16 +3107,16 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
>   */
>  void split_page_memcg(struct page *first, unsigned order)
>  {
> -	struct folio *folio = page_folio(first);
> +	struct obj_cgroup *objcg = page_objcg(first);
>  	unsigned int i, nr = 1 << order;
>  
> -	if (mem_cgroup_disabled() || !folio_memcg_charged(folio))
> +	if (!objcg)
>  		return;

mem_cgroup_disabled() is a jump label, so a bit cheaper than the
branch. Can you keep that and do page_objcg() after it?

>  	for (i = 1; i < nr; i++)
> -		folio_page(folio, i)->memcg_data = folio->memcg_data;
> +		page_set_objcg(&first[i], objcg);
>  
> -	obj_cgroup_get_many(__folio_objcg(folio), nr - 1);
> +	obj_cgroup_get_many(objcg, nr - 1);
>  }

This is much nicer indeed. Thanks for doing this.

With the above nits considered,

Acked-by: Johannes Weiner <hannes@cmpxchg.org>