Re: [PATCH 03/17] mm/sparse-vmemmap: introduce folio-oriented vmemmap optimization macros

[Mike Rapoport]

> Introduce macros for those folio-oriented properties and use them to
> replace the tail-based names in the HVO paths. This makes the code read
> in terms of folio semantics instead of an implementation detail and
> better matches other folio-based users such as DAX.
> 
> No functional change intended.
> 
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index bacd89572c5c..ea884245f499 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -107,13 +107,15 @@
>  	 is_power_of_2(sizeof(struct page)) ? \
>  	 MAX_FOLIO_NR_PAGES * sizeof(struct page) : 0)
>  
> -/*
> - * vmemmap optimization (like HVO) is only possible for page orders that fill
> - * two or more pages with struct pages.
> - */
> -#define VMEMMAP_TAIL_MIN_ORDER (ilog2(2 * PAGE_SIZE / sizeof(struct page)))
> -#define __NR_VMEMMAP_TAILS (MAX_FOLIO_ORDER - VMEMMAP_TAIL_MIN_ORDER + 1)
> -#define NR_VMEMMAP_TAILS (__NR_VMEMMAP_TAILS > 0 ? __NR_VMEMMAP_TAILS : 0)
> +/* The number of vmemmap pages required by a vmemmap-optimized folio. */
> +#define OPTIMIZED_FOLIO_VMEMMAP_PAGES		1
> +#define OPTIMIZED_FOLIO_VMEMMAP_SIZE		(OPTIMIZED_FOLIO_VMEMMAP_PAGES * PAGE_SIZE)
> +#define OPTIMIZED_FOLIO_VMEMMAP_NR_STRUCT_PAGES	(OPTIMIZED_FOLIO_VMEMMAP_SIZE / sizeof(struct page))
> +#define OPTIMIZABLE_FOLIO_MIN_ORDER		(ilog2(OPTIMIZED_FOLIO_VMEMMAP_NR_STRUCT_PAGES) + 1)
> +
> +#define __NR_OPTIMIZABLE_FOLIO_ORDERS		(MAX_FOLIO_ORDER - OPTIMIZABLE_FOLIO_MIN_ORDER + 1)
> +#define NR_OPTIMIZABLE_FOLIO_ORDERS		\
> +	(__NR_OPTIMIZABLE_FOLIO_ORDERS > 0 ? __NR_OPTIMIZABLE_FOLIO_ORDERS : 0)

I can't say I like the new names, they read like some folio optimization
rather than vmemmap optimization.

I think they should be namespaced with VMEMMAP_ or even
VMEMMAP_OPTIMIZATION_ (or VMEMMAP_OPT_) and should not mention folio.

I'd also drop intermediate defines OPTIMIZED_FOLIO_VMEMMAP_PAGES and
OPTIMIZED_FOLIO_VMEMMAP_SIZE and use 1 and PAGE_SIZE directly.

-- 
Sincerely yours,
Mike.