Subject: Re: [PATCH v4 1/7] mm: page_alloc: avoid merging non-fallbackable pageblocks with others.

From: Mel Gorman <[email-masked]>
Date: Mon, 24 Jan 2022 14:02:03 +0000

On Wed, Jan 19, 2022 at 02:06:17PM -0500, Zi Yan wrote:
> From: Zi Yan <[email-masked]>
> 
> This is done in addition to MIGRATE_ISOLATE pageblock merge avoidance.
> It prepares for the upcoming removal of the MAX_ORDER-1 alignment
> requirement for CMA and alloc_contig_range().
> 
> MIGRARTE_HIGHATOMIC should not merge with other migratetypes like
> MIGRATE_ISOLATE and MIGRARTE_CMA[1], so this commit prevents that too.
> Also add MIGRARTE_HIGHATOMIC to fallbacks array for completeness.
> 
> [1] https://lore.kernel.org/linux-mm/[email-masked]/
> 
> Signed-off-by: Zi Yan <[email-masked]>
>
> <SNIP>
>
> @@ -2484,6 +2483,7 @@ 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 },
> +	[MIGRATE_HIGHATOMIC] = { MIGRATE_TYPES }, /* Never used */
>  #ifdef CONFIG_CMA
>  	[MIGRATE_CMA]         = { MIGRATE_TYPES }, /* Never used */
>  #endif

If it's never used, why is it added?

Otherwise looks fine so

Acked-by: Mel Gorman <[email-masked]>

-- 
Mel Gorman
SUSE Labs