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