if (!pfn_valid(page_to_pfn(page)) || PageReserved(page)) return;
BUG_ON(!pfn_valid(page_to_pfn(page)));
void page_add_file_rmap(struct page *page){	BUG_ON(PageAnon(page));	if (!pfn_valid(page_to_pfn(page)) || PageReserved(page))		return;	if (atomic_inc_and_test(&page->_mapcount))		inc_page_state(nr_mapped);}