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

["David Hildenbrand (Red Hat)" <david@kernel.org>]

On 01.11.25 03:11, 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 before
> proceeding with further validation.
> 
> This commit unifies the logic by introducing a new variable,
> @need_check, which is conditionally set based on whether a uniform
> split is requested. This allows us to 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>
> ---
>   include/linux/huge_mm.h |  8 +++---
>   mm/huge_memory.c        | 55 +++++++++++------------------------------
>   2 files changed, 18 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 d1fa0d2d9b44..f6d2cb2a5ca0 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3673,55 +3673,34 @@ 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)

Likely a simple

enum split_type {
	SPLIT_TYPE_UNIFORM,
	SPLIT_TYPE_NON_UNIFORM, // or SPLIT_TYPE_BUDDY?
};

Could make invocations easier to read.

>   {
> -	if (folio_test_anon(folio)) {
> -		/* order-1 is not supported for anonymous THP. */
> -		VM_WARN_ONCE(warns && new_order == 1,
> -				"Cannot split to order-1 folio");
> -		return new_order != 1;
> -	} else if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
> -	    !mapping_large_folio_support(folio->mapping)) {
> -		/*
> -		 * No split if the file system does not support large folio.
> -		 * Note that we might still have THPs in such mappings due to
> -		 * CONFIG_READ_ONLY_THP_FOR_FS. But in that case, the mapping
> -		 * does not actually support large folios properly.
> -		 */
> -		VM_WARN_ONCE(warns,
> -			"Cannot split file folio to non-0 order");
> -		return false;
> -	}
> -
> -	/* Only swapping a whole PMD-mapped folio is supported */
> -	if (folio_test_swapcache(folio)) {
> -		VM_WARN_ONCE(warns,
> -			"Cannot split swapcache folio to non-0 order");
> -		return false;
> -	}
> +	bool need_check = uniform_split ? new_order : true;

(could be const)

Not really a great name for that variable (what needs a check?).  Maybe 
simply ...



>   
> -	return true;
> -}
> -
> -/* See comments in non_uniform_split_supported() */
> -bool uniform_split_supported(struct folio *folio, unsigned int new_order,
> -		bool warns)
> -{
>   	if (folio_test_anon(folio)) {
> +		/* order-1 is not supported for anonymous THP. */
>   		VM_WARN_ONCE(warns && new_order == 1,
>   				"Cannot split to order-1 folio");
>   		return new_order != 1;
> -	} else  if (new_order) {
> +	} else if (need_check) {

... change this to ("!uniform_split || new_order")

} else if (!uniform_split || new_order) {