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

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

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.

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.

>  	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
>
>