During folio migration, __folio_migrate_mapping() removes the source folio from the deferred split queue, but the destination folio is never re-queued. This causes underutilized THPs to escape the shrinker after NUMA migration, since they silently drop off the deferred split list. Fix this by calling deferred_split_folio() on the destination folio after a successful migration, for large rmappable folios. Reported-by: Johannes Weiner Fixes: dafff3f4c850 ("mm: split underused THPs") Signed-off-by: Usama Arif --- mm/migrate.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/mm/migrate.c b/mm/migrate.c index ece77ccb2ec0..98d0a594f7b7 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1393,6 +1393,17 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private, if (old_page_state & PAGE_WAS_MAPPED) remove_migration_ptes(src, dst, 0); + /* + * Requeue the destination folio on the deferred split queue if + * the source was a large folio that was on the queue. Without + * this, NUMA migration causes underutilized THPs to escape + * the shrinker since the source is unqueued in + * __folio_migrate_mapping() and the destination is never + * re-queued. + */ + if (folio_test_large(dst) && folio_test_large_rmappable(dst)) + deferred_split_folio(dst, false); + out_unlock_both: folio_unlock(dst); folio_set_owner_migrate_reason(dst, reason); -- 2.47.3