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

[David Hildenbrand (Arm)]

On 7/14/26 15:09, Vlastimil Babka (SUSE) wrote:
> 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.

Right, it's a placeholder for "there is no migrate reason because it is unset"

> So I think the name is more descriptive this way.

Not sure I agree. The usual translation of -1 -> unset is NONE or UNSET.

At least I was confused by "NEVER".

-- 
Cheers,

David