Re: [PATCH 2/2] mm/mm.h: Write folio->_flags_1 & 0xff as a macro definition

[liuye <liuye@kylinos.cn>]

在 2025/2/12 13:12, Dev Jain 写道:
> 
> 
> On 12/02/25 8:28 am, Liu Ye wrote:
>> There are multiple locations in mm.h where (folio->_flags_1 & 0xff) is
>> used. Write it as a macro definition to improve the readability and
>> maintainability of the code.
>>
>> Signed-off-by: Liu Ye <liuye@kylinos.cn>
>> ---
>>   include/linux/mm.h | 10 ++++++----
>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 7b1068ddcbb7..750e75f45557 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1098,6 +1098,8 @@ int vma_is_stack_for_current(struct vm_area_struct *vma);
>>   struct mmu_gather;
>>   struct inode;
>>   +#define FOLIO_ORDER(folio) ((folio)->_flags_1 & 0xff)
>> +
>>   /*
>>    * compound_order() can be called without holding a reference, which means
>>    * that niceties like page_folio() don't work.  These callers should be
>> @@ -1111,7 +1113,7 @@ static inline unsigned int compound_order(struct page *page)
>>         if (!test_bit(PG_head, &folio->flags))
>>           return 0;
>> -    return folio->_flags_1 & 0xff;
>> +    return FOLIO_ORDER(folio);
>>   }
>>     /**
>> @@ -1127,7 +1129,7 @@ static inline unsigned int folio_order(const struct folio *folio)
>>   {
>>       if (!folio_test_large(folio))
>>           return 0;
>> -    return folio->_flags_1 & 0xff;
>> +    return FOLIO_ORDER(folio);
>>   }
>>     #include <linux/huge_mm.h>
>> @@ -2061,7 +2063,7 @@ static inline long folio_nr_pages(const struct folio *folio)
>>   #ifdef CONFIG_64BIT
>>       return folio->_folio_nr_pages;
>>   #else
>> -    return 1L << (folio->_flags_1 & 0xff);
>> +    return 1L << FOLIO_ORDER(folio);
>>   #endif
>>   }
>>   @@ -2086,7 +2088,7 @@ static inline unsigned long compound_nr(struct page *page)
>>   #ifdef CONFIG_64BIT
>>       return folio->_folio_nr_pages;
>>   #else
>> -    return 1L << (folio->_flags_1 & 0xff);
>> +    return 1L << FOLIO_ORDER(folio);
>>   #endif
>>   }
>>   
> 
> Personally I do not think this is improving readability. You are introducing one more macro for people to decipher instead of directly seeing folio->_flags_1 & 0xff. This is similar to whether to write
> if (x) => do_stuff(), or if (x != 0) => do_stuff(). The former is more "readable" by convention but the latter makes it easier and obvious to understand.
> 
Or simply for maintenance purposes, if the meaning of a bit changes, only the macro definition needs to be modified.

Thanks，
Liu Ye