Re: [Patch v2] mm/huge_memory: merge uniform_split_supported() and non_uniform_split_supported()

[Zi Yan <ziy@nvidia.com>]

On 5 Nov 2025, at 2:25, Wei Yang wrote:

> The functions uniform_split_supported() and
> non_uniform_split_supported() share significantly similar logic.
>
> The only functional difference is that uniform_split_supported()
> includes an additional check on the requested @new_order.
>
> The reason for this check comes from the following two aspects:
>
>   * some file system or swap cache just supports order-0 folio
>   * the behavioral difference between uniform/non-uniform split
>
> The behavioral difference between uniform split and non-uniform:
>
>   * uniform split splits folio directly to @new_order
>   * non-uniform split creates after-split folios with orders from
>     folio_order(folio) - 1 to new_order.
>
> This means for non-uniform split or !new_order split we should check the
> file system and swap cache respectively.
>
> This commit unifies the logic and merge the two functions into a single
> combined helper, removing redundant code and simplifying the split
> support checking mechanism.
>
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: "David Hildenbrand (Red Hat)" <david@kernel.org>
>
> ---
> v2:
>   * remove need_check
>   * update comment
>   * add more explanation in change log
>   * selftests/split_huge_page_test pass
> ---
>  include/linux/huge_mm.h |  8 ++---
>  mm/huge_memory.c        | 70 ++++++++++++++++++-----------------------
>  2 files changed, 33 insertions(+), 45 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index cbb2243f8e56..79343809a7be 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -369,10 +369,8 @@ int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list
>  		unsigned int new_order, bool unmapped);
>  int min_order_for_split(struct folio *folio);
>  int split_folio_to_list(struct folio *folio, struct list_head *list);
> -bool uniform_split_supported(struct folio *folio, unsigned int new_order,
> -		bool warns);
> -bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
> -		bool warns);
> +bool folio_split_supported(struct folio *folio, unsigned int new_order,
> +		bool uniform_split, bool warns);
>  int folio_split(struct folio *folio, unsigned int new_order, struct page *page,
>  		struct list_head *list);
>
> @@ -403,7 +401,7 @@ static inline int split_huge_page_to_order(struct page *page, unsigned int new_o
>  static inline int try_folio_split_to_order(struct folio *folio,
>  		struct page *page, unsigned int new_order)
>  {
> -	if (!non_uniform_split_supported(folio, new_order, /* warns= */ false))
> +	if (!folio_split_supported(folio, new_order, /* uniform_split = */ false, /* warns= */ false))
>  		return split_huge_page_to_order(&folio->page, new_order);
>  	return folio_split(folio, new_order, page, NULL);
>  }
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 381a49c5ac3f..db442e0e3a46 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3666,55 +3666,49 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
>  	return 0;
>  }
>
> -bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
> -		bool warns)
> +bool folio_split_supported(struct folio *folio, unsigned int new_order,
> +		bool uniform_split, bool warns)

For this one, David suggested to use a enum

enum split_type {
	SPLIT_TYPE_UNIFORM,
	SPLIT_TYPE_NON_UNIFORM,
};

in a separate cleanup patch. It is better to send it along with this
one, so that:

1. it will be easy for reviewers to keep track of both changes,
2. it also helps resolve the dependency issue, where the cleanup patch
   goes after this one.

Thanks.


Best Regards,
Yan, Zi