Re: [PATCH mm-unstable] mm: clarify folio_set_compound_order() zero support

[John Hubbard <jhubbard@nvidia.com>]

On 12/8/22 13:58, Sidhartha Kumar wrote:
> Thanks John, Mike, Matthew, and Muchun for the feedback.
> 
> To summarize this discussion and outline the next version of this patch, the changes I'll make include:
> 
> 1) change the name of folio_set_compound_order() to folio_set_order()
> 2) change the placement of this function from mm.h to mm/internal.h
> 3) folio_set_order() will set both _folio_order and _folio_nr_pages and handle the zero order case correctly.
> 4) remove the comment about hugetlb's specific use for zero orders
> 5) improve the style of folio_set_order() by removing ifdefs from inside the function to doing
> 
> #ifdef CONFIG_64BIT
>   static inline void folio_set_order(struct folio *folio,
>                   unsigned int order)
>   {
>       VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);

Sounds good, except for this part: why is a function named
folio_set_order() BUG-ing on a non-large folio? The naming
is still wrong, perhaps?

> 
>       folio->_folio_order = order;
>           folio->_folio_nr_pages = order ? 1U << order : 0;
> }
> #else
> static inline void folio_set_order(struct folio *folio,
>                   unsigned int order)
>   {
>       VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
> 
>       folio->_folio_order = order;
> }
> #endif
> 
> Please let me know if I missing something.
> Thanks,
> Sidhartha Kumar
>> Thanks,
> 

thanks,
-- 
John Hubbard
NVIDIA