bm_bit_to_page_idx
p_addr = __bm_map_pidx(b, bm_bit_to_page_idx(b, bm_fo));
unsigned int page_nr = bm_bit_to_page_idx(b, bitnr);
p_addr = bm_map_pidx(b, bm_bit_to_page_idx(b, bitnr));
unsigned int idx = bm_bit_to_page_idx(b, bitnr);