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

[Matthew Wilcox]

On Thu, Feb 27, 2025 at 05:55:43AM +0000, Matthew Wilcox wrote:
> 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

umm, old_order - new_order.  Anyway, here's a patch I've done on top of
your work, but it probably needs to be massaged slightly and placed
before your work?