Re: [PATCH v6 2/9] mm/page_owner: add MR_NEVER to enum migrate_reason and use it for last_migrate_reason

[Vlastimil Babka (SUSE)]

On 7/14/26 15:05, David Hildenbrand (Arm) wrote:
> On 7/14/26 03:51, Ye Liu wrote:
>> The last_migrate_reason field uses -1 as a sentinel value to mean "no
>> migration has happened".  Replace the four bare -1 occurrences by
>> adding a proper MR_NEVER member to enum migrate_reason, defining a
>> corresponding "never_migrated" string in the MIGRATE_REASON trace
>> macro, and updating the GDB page_owner script to use MR_NEVER instead
>> of the hardcoded -1 so that lx-dump-page-owner does not incorrectly
>> report unmigrated pages as migrated.
>> 
>> No functional change.
>> 
>> Signed-off-by: Ye Liu <ye.liu@xxxxxxxxx>
>> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
>> Reviewed-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
>> ---
>>  include/linux/migrate_mode.h    | 1 +
>>  include/trace/events/migrate.h  | 3 ++-
>>  mm/page_owner.c                 | 8 ++++----
>>  scripts/gdb/linux/page_owner.py | 4 +++-
>>  4 files changed, 10 insertions(+), 6 deletions(-)
>> 
>> diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
>> index 265c4328b36a..05102d4d2490 100644
>> --- a/include/linux/migrate_mode.h
>> +++ b/include/linux/migrate_mode.h
>> @@ -25,6 +25,7 @@ enum migrate_reason {
>>  	MR_LONGTERM_PIN,
>>  	MR_DEMOTION,
>>  	MR_DAMON,
>> +	MR_NEVER,		/* page has never been migrated */
> 
> Shouldn't this be more like
> 
> "MR_NONE" ?
> 
> As "never" is not really a "reason" ?

It's not used ever as a reason that would be actually passed to migration.
So I think the name is more descriptive this way.