Re: [Patch v3 4/4] mm/huge_memory: optimize old_order derivation during folio splitting

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

On Thu, Oct 30, 2025 at 09:55:18PM -0400, Zi Yan wrote:
>On 30 Oct 2025, at 21:50, Wei Yang wrote:
>
>> On Fri, Oct 24, 2025 at 11:29:00AM -0400, Zi Yan wrote:
>>> On 24 Oct 2025, at 10:46, Lorenzo Stoakes wrote:
>> [...]
>>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>>>> index 093b3ffb180f..a4fa8b0e5b5a 100644
>>>>> --- a/mm/huge_memory.c
>>>>> +++ b/mm/huge_memory.c
>>>>> @@ -3596,8 +3596,8 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
>>>>>  		struct address_space *mapping, bool uniform_split)
>>>>>  {
>>>>>  	const bool is_anon = folio_test_anon(folio);
>>>>> -	int order = folio_order(folio);
>>>>> -	int start_order = uniform_split ? new_order : order - 1;
>>>>> +	int old_order = folio_order(folio);
>>>>> +	int start_order = uniform_split ? new_order : old_order - 1;
>>>>>  	int split_order;
>>>>>
>>>>>  	folio_clear_has_hwpoisoned(folio);
>>>>> @@ -3609,14 +3609,11 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
>>>>>  	for (split_order = start_order;
>>>>>  	     split_order >= new_order;
>>>>
>>>> A thought for the future - now things are simplified, it might be nice to just
>>>> separate out the core of this loop and have the uniform split just call the
>>>> split out function directly, and the non-uniform one do the loop.
>>>>
>>>> As it's a bit gross in the uniform case we just let split_order go to new_order
>>>> - 1 to exit the loop.
>>>
>>> Yeah, something like:
>>>
>>> if (uniform_split) {
>>> 	if (mapping)
>>> 		xas_split(xas, folio, old_order);
>>> 	split_folio_to_order(...);
>>> 	return 0;
>>> }
>>>
>>> for () {
>>> ...
>>> split_folio_to_order(...);
>>> ...
>>> }
>>>
>>> where split_folio_to_order(...) just
>>> split memcg, split page owner, pgalloc_tag_split, __split_folio_to_order,
>>> and stats update
>>>
>>
>> This looks reasonable, while I found we already have split_folio_to_order().
>
>Then, we just need a new name, like __split_folio_and_update_stats().
>I am bad at naming. Feel free to come up with a better one. :)
>

Ok, let me have a try ... not good at it neither.


-- 
Wei Yang
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