page_completion_from_waiter
vdo_fail_completion(&page_completion_from_waiter(waiter)->completion, *result);
complete_with_page(page_info, page_completion_from_waiter(waiter));
return (page_completion_from_waiter(waiter)->pbn == *pbn);
pbn = page_completion_from_waiter(oldest_waiter)->pbn;