PD_PTDESC
#define PD_MARKBITS(dp) (*(unsigned int *)&PD_PTDESC(dp)->pt_index)
__ClearPageReserved(ptdesc_page(PD_PTDESC(dp)));
init_page_count(ptdesc_page(PD_PTDESC(dp)));
return ptdesc_address(PD_PTDESC(dp)) + off;