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

[Wei Yang <richard.weiyang@gmail.com>]

On Wed, Nov 05, 2025 at 11:41:35AM -0500, Zi Yan wrote:
>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.

Sure, will add it.

>
>
>Best Regards,
>Yan, Zi

-- 
Wei Yang
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