Re: [PATCH] mm/page_alloc: reduce fallbacks to (MIGRATE_PCPTYPES - 1)

[Andrew Morton <akpm@linux-foundation.org>]

On Fri,  3 Feb 2023 18:01:32 +0800 Yajun Deng <yajun.deng@linux.dev> wrote:

> The commit 1dd214b8f21c ("mm: page_alloc: avoid merging non-fallbackable
> pageblocks with others") has removed MIGRATE_CMA and MIGRATE_ISOLATE from
> fallbacks list. so there is no need to add an element at the end of every
> type.
> 
> Reduce fallbacks to (MIGRATE_PCPTYPES - 1).

Thanks.  `git log' suggests who should be cc'ed when fixing things...

> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2603,10 +2603,10 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>   *
>   * The other migratetypes do not have fallbacks.
>   */
> -static int fallbacks[MIGRATE_TYPES][3] = {
> -	[MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE,   MIGRATE_TYPES },
> -	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
> -	[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE,   MIGRATE_TYPES },
> +static int fallbacks[MIGRATE_TYPES][MIGRATE_PCPTYPES - 1] = {
> +	[MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE   },
> +	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
> +	[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE   },
>  };
>  
>  #ifdef CONFIG_CMA
> @@ -2865,11 +2865,8 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>  		return -1;
>  
>  	*can_steal = false;
> -	for (i = 0;; i++) {
> +	for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
>  		fallback_mt = fallbacks[migratetype][i];
> -		if (fallback_mt == MIGRATE_TYPES)
> -			break;
> -
>  		if (free_area_empty(area, fallback_mt))
>  			continue;
>  
> -- 
> 2.25.1