Re: [PATCH 4/4] mm/page_alloc: remove ifdefs from pindex helpers

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 5/13/26 14:35, Brendan Jackman wrote:
> The ifdefs are not technically needed here, everything used here is
> always defined.
> 
> Switching to IS_ENABLED() makes the code a bit less tiresome to read.
> 
> Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>  mm/page_alloc.c | 30 ++++++++++++++----------------
>  1 file changed, 14 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5d6144c8860ed10fd641184f389c4953465d5178..2985ad0ab1044bdfda8ccc7aaed2ded19b5ac7ed 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -650,19 +650,17 @@ static void bad_page(struct page *page, const char *reason)
>  
>  static inline unsigned int order_to_pindex(int migratetype, int order)
>  {
> +	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
> +		bool movable = migratetype == MIGRATE_MOVABLE;
>  
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	bool movable;
> -	if (order > PAGE_ALLOC_COSTLY_ORDER) {
> -		VM_BUG_ON(!is_pmd_order(order));
> +		if (order > PAGE_ALLOC_COSTLY_ORDER) {
> +			VM_BUG_ON(!is_pmd_order(order));
>  
> -		movable = migratetype == MIGRATE_MOVABLE;
> -
> -		return NR_LOWORDER_PCP_LISTS + movable;
> +			return NR_LOWORDER_PCP_LISTS + movable;
> +		}
> +	} else {
> +		VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
>  	}
> -#else
> -	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
> -#endif

Uh yeah, VM_BUG_ONs are frowned upon now. But doing a VM_WARN_ON_ONCE here
makes little sense. There's no safe fallback if we end up here with a wrong
value. And it's all internal to page alloc so I'd just drop those checks
completely at this point.

>  	return (MIGRATE_PCPTYPES * order) + migratetype;
>  }
> @@ -671,12 +669,12 @@ static inline int pindex_to_order(unsigned int pindex)
>  {
>  	int order = pindex / MIGRATE_PCPTYPES;
>  
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	if (pindex >= NR_LOWORDER_PCP_LISTS)
> -		order = HPAGE_PMD_ORDER;
> -#else
> -	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
> -#endif
> +	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
> +		if (pindex >= NR_LOWORDER_PCP_LISTS)
> +			order = HPAGE_PMD_ORDER;
> +	} else {
> +		VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
> +	}
>  
>  	return order;
>  }
>