why does the function page_to_nid always return zero?

why does the function page_to_nid always return zero?

[Hua Feijun]

Hi everybody:
Tthe following code deoes not work under linux/em64t, and the function
page_to_nid always return zero.Who can tell me the answer to the
problem?
Any advice will be appreciated sincerely.Thanks!!!

pgd = pgd_offset(mm, vaddr);
 if (pgd == NULL) {
   return -1;
 }
 pmd = pmd_offset(pgd, vaddr);
 if (pmd == NULL) {
     return -2;
 }
 pte = pte_offset_map(pmd, vaddr);
 PDEBUG("pte=%ul\n", pte->pte);
 if (pte == NULL) {
    return -3;
 }
return page_to_nid (page);
 if (pte_present(*pte) == NULL) {
    return -4;
 }
 page = pte_page(*pte);
 pte_unmap(pte);

return page_to_nid(page);