Simplify new_page() by unifying the THP and base page cases, and
handle orders other than 0 and HPAGE_PMD_ORDER correctly.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NZi Yan <ziy@nvidia.com>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>