Re: [PATCH 1/2] mm: page_alloc: do not give all non-blocking requests reserve access

[Matthew Wilcox]

On Mon, Sep 21, 2026 at 10:38:18AM -0400, Johannes Weiner wrote:
> +++ b/mm/page_alloc.c
> @@ -3246,7 +3246,9 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
>  			 * reserves as failing now is worse than failing a
>  			 * high-order atomic allocation in the future.
>  			 */
> -			if (!page && (alloc_flags & (ALLOC_OOM|ALLOC_NON_BLOCK)))
> +			if (!page &&
> +			    ((alloc_flags & ALLOC_OOM) ||
> +			     (alloc_flags & ALLOC_MASK_ATOMIC) == ALLOC_MASK_ATOMIC))
>  				page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);

Would this be slightly neater?

static inline bool may_access_reserves(unsigned int alloc_flags)
{
	if (alloc_flags & ALLOC_OOM)
		return true;
	if (alloc_flags & (ALLOC_NON_BLOCK | ALLOC_MIN_RESERVE)) ==
	    (ALLOC_NON_BLOCK | ALLOC_MIN_RESERVE)
		return true;
	return false;
}

[...]

-			if (!page && (alloc_flags & (ALLOC_OOM|ALLOC_NON_BLOCK)))
+			if (!page && may_access_reserves(alloc_flags))
 				page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);