mm/page_alloc: remove VM_BUG_ON()s from pindex helpers

[PATCH v2] mm/page_alloc: remove VM_BUG_ON()s from pindex helpers

Posted by Brendan Jackman 1 week, 6 days ago

Vlastimil pointed out that the VM_BUG_ON()s have fallen out of
favour, so remove them.

Suggested-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Link: https://lore.kernel.org/all/4074a816-9e75-45a6-8141-25459bcc106b@kernel.org/
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
Changes in v2:
- Rebased onto mm-new, removed VM_BUG_ON()s
- Link to v1: https://lore.kernel.org/r/20260513-page_alloc-unmapped-prep-v1-0-dacdf5402be8@google.com
---
 mm/page_alloc.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1b5b1e556f76feadf21f3f44a9440fe883fb7651..e47679e7a9dbc772aa27f550a10aa8c0e95af55a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -653,13 +653,8 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
 	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
 		bool movable = migratetype == MIGRATE_MOVABLE;
 
-		if (order > PAGE_ALLOC_COSTLY_ORDER) {
-			VM_BUG_ON(!is_pmd_order(order));
-
+		if (order > PAGE_ALLOC_COSTLY_ORDER)
 			return NR_LOWORDER_PCP_LISTS + movable;
-		}
-	} else {
-		VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
 	}
 
 	return (MIGRATE_PCPTYPES * order) + migratetype;
@@ -672,8 +667,6 @@ static inline int pindex_to_order(unsigned int pindex)
 	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;

---
base-commit: da0a06486ac3ce47c6ffb603d2fd332229d41592
change-id: 20260512-page_alloc-unmapped-prep-c3ae0381d58b

Best regards,
-- 
Brendan Jackman <jackmanb@google.com>

Re: [PATCH v2] mm/page_alloc: remove VM_BUG_ON()s from pindex helpers

Posted by Vlastimil Babka (SUSE) 1 week, 6 days ago

On 5/26/26 1:28 PM, Brendan Jackman wrote:
> Vlastimil pointed out that the VM_BUG_ON()s have fallen out of
> favour, so remove them.
> 
> Suggested-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> Link: https://lore.kernel.org/all/4074a816-9e75-45a6-8141-25459bcc106b@kernel.org/
> Signed-off-by: Brendan Jackman <jackmanb@google.com>

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Thanks.

> ---
> Changes in v2:
> - Rebased onto mm-new, removed VM_BUG_ON()s
> - Link to v1: https://lore.kernel.org/r/20260513-page_alloc-unmapped-prep-v1-0-dacdf5402be8@google.com
> ---
>  mm/page_alloc.c | 9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1b5b1e556f76feadf21f3f44a9440fe883fb7651..e47679e7a9dbc772aa27f550a10aa8c0e95af55a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -653,13 +653,8 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
>  	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
>  		bool movable = migratetype == MIGRATE_MOVABLE;
>  
> -		if (order > PAGE_ALLOC_COSTLY_ORDER) {
> -			VM_BUG_ON(!is_pmd_order(order));
> -
> +		if (order > PAGE_ALLOC_COSTLY_ORDER)
>  			return NR_LOWORDER_PCP_LISTS + movable;
> -		}
> -	} else {
> -		VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
>  	}
>  
>  	return (MIGRATE_PCPTYPES * order) + migratetype;
> @@ -672,8 +667,6 @@ static inline int pindex_to_order(unsigned int pindex)
>  	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;
> 
> ---
> base-commit: da0a06486ac3ce47c6ffb603d2fd332229d41592
> change-id: 20260512-page_alloc-unmapped-prep-c3ae0381d58b
> 
> Best regards,