Re: [Patch v2 1/2] mm/huge_memory: cache folio attribute in __split_unmapped_folio()

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

On Fri, Oct 17, 2025 at 10:46:43AM +0100, Lorenzo Stoakes wrote:
>I don't like 'cache' here. You're not cache-ing anything, you're relying on an
>attribute remaining constant.
>
>Something like 'avoid reinvoking folio_test_anon()' would be simpler.
>

Will adjust it.

>On Thu, Oct 16, 2025 at 12:46:12AM +0000, Wei Yang wrote:
>> During the execution of __split_unmapped_folio(), the folio's anon/!anon
>> attribute is invariant (not expected to change).
>>
>> Therefore, it is safe and more efficient to retrieve this attribute once
>> at the start and reuse it throughout the function.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> Cc: Zi Yan <ziy@nvidia.com>
>> Reviewed-by: Zi Yan <ziy@nvidia.com>
>> Reviewed-by: wang lian <lianux.mm@gmail.com>
>> ---
>>  mm/huge_memory.c | 7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 3c74227cc847..4b2d5a7e5c8e 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -3527,6 +3527,7 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
>>  		struct page *split_at, struct xa_state *xas,
>>  		struct address_space *mapping, bool uniform_split)
>>  {
>> +	bool is_anon = folio_test_anon(folio);
>
>As David said, make this const please.
>

Will do.

>>  	int order = folio_order(folio);
>>  	int start_order = uniform_split ? new_order : order - 1;
>>  	bool stop_split = false;
>> @@ -3534,7 +3535,7 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
>>  	int split_order;
>>  	int ret = 0;
>>
>> -	if (folio_test_anon(folio))
>> +	if (is_anon)
>>  		mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
>>
>>  	folio_clear_has_hwpoisoned(folio);
>> @@ -3551,7 +3552,7 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
>>  		struct folio *new_folio;
>>
>>  		/* order-1 anonymous folio is not supported */
>> -		if (folio_test_anon(folio) && split_order == 1)
>> +		if (is_anon && split_order == 1)
>>  			continue;
>>  		if (uniform_split && split_order != new_order)
>>  			continue;
>> @@ -3603,7 +3604,7 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
>>  				if (split_order != new_order && !stop_split)
>>  					continue;
>>  			}
>> -			if (folio_test_anon(new_folio))
>> +			if (is_anon)
>>  				mod_mthp_stat(folio_order(new_folio),
>>  					      MTHP_STAT_NR_ANON, 1);
>>  		}
>> --
>> 2.34.1
>>
>>

-- 
Wei Yang
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