(gdb) ptype /o struct m_ext
/* offset    |  size */  type = struct m_ext {
/*    0      |     4 */    union {
/*                 4 */        volatile u_int ext_count;
/*                 4 */        volatile u_int *ext_cnt;

                               /* total size (bytes):    4 */
                           };
/*    4      |     4 */    uint32_t ext_size;
/*    8: 0   |     4 */    uint32_t ext_type : 8;
/*    9: 0   |     4 */    uint32_t ext_flags : 24;
/* XXX  4-byte hole  */
/*   16      |   160 */    union {
/*                 8 */        struct {
/*   16      |     4 */            char *ext_buf;
/*   20      |     4 */            void *ext_arg2;

                                   /* total size (bytes):    8 */
                               };
/*               160 */        struct {
/*   16      |    72 */            vm_paddr_t extpg_pa[9];
/*   88      |    64 */            char extpg_trail[64];
/*  152      |    23 */            char extpg_hdr[23];
/* XXX  1-byte padding  */

                                   /* total size (bytes):  160 */
                               };
/* XXX 144-byte padding  */

                               /* total size (bytes):  160 */
                           };
/*  176      |     4 */    m_ext_free_t *ext_free;
/*  180      |     4 */    void *ext_arg1;

                           /* total size (bytes):  184 */
                         }