On 24 Jan 2022, at 9:02, Mel Gorman wrote:

> On Wed, Jan 19, 2022 at 02:06:17PM -0500, Zi Yan wrote:
>> From: Zi Yan <ziy@nvidia.com>
>>
>> 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/20211130100853.GP3366@techsingularity.net/
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>>
>> <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?

Just to make the fallbacks list complete, since MIGRATE_CMA and
MIGRATE_ISOLATE are in the list. Instead, I can remove MIGRATE_CMA and
MIGRATE_ISOLATE. WDYT?

>
> Otherwise looks fine so
>
> Acked-by: Mel Gorman <mgorman@techsingularity.net>

Thanks.

--
Best Regards,
Yan, Zi