Re: [PATCH v9 2/8] mm/huge_memory: add two new (not yet used) functions for folio_split()

[Matthew Wilcox]

On Wed, Feb 26, 2025 at 04:00:25PM -0500, Zi Yan wrote:
> +static int __split_unmapped_folio(struct folio *folio, int new_order,
> +		struct page *split_at, struct page *lock_at,
> +		struct list_head *list, pgoff_t end,
> +		struct xa_state *xas, struct address_space *mapping,
> +		bool uniform_split)
> +{
[...]
> +		/* complete memcg works before add pages to LRU */
> +		split_page_memcg(&folio->page, old_order, split_order);
> +		split_page_owner(&folio->page, old_order, split_order);
> +		pgalloc_tag_split(folio, old_order, split_order);

At least split_page_memcg() needs to become aware of 'uniform_split'.

        if (folio_memcg_kmem(folio))
                obj_cgroup_get_many(__folio_objcg(folio), old_nr / new_nr - 1);

If we're doing uniform_split, that calculation should be
	old_order - new_order - 1