page_pgoff
key->shared.pgoff = page_pgoff(folio, page);
pgoff = page_pgoff(folio, page);
pgoff = page_pgoff(folio, page);
pvmw.address = vma_address(vma, page_pgoff(folio, page), 1);
VM_BUG_ON_PAGE(page_pgoff(folio, page) != linear_page_index(vma, address),
return vma_address(vma, page_pgoff(folio, page), 1);