Hi Naoya,
I encounter the issue that page migration fails due to page ref count != 1 thus return -EAGAIN in migrate_page_move_mapping().
And it turns out that in page fault handling, __migration_entry_wait() calls get_page_unless_zero() to get an extra ref count before wait_on_page_locked().
Is there a fix that can safely wait for migration to complete without taking the ref on page?
Thanks.
-Zhan