On Tue, Mar 30, 2021 at 04:42:00PM +0200, Gerald Schaefer wrote:

Could there be a work-around by splitting THP pages instead of marking them
as migrate pmds (via pte swap entries), at least when THP migration is not
supported? I guess it could also be acceptable if THP pages were simply not
migrated for NUMA balancing on s390, but then we might need some extra config
option to make that behavior explicit.

The split is not done on other architectures simply because the loss
from splitting exceeded the gain of improved locality in too many cases.
However, it might be ok as an s390-specific workaround.

(Note, I haven't read the rest of the series due to lack of time but this
query caught my eye).

-- 
Mel Gorman
SUSE Labs