mm: store compound_dtor / compound_order as bytes

Neither of these values get even close to 256; compound_dtor is
currently at a maximum of 3, and compound_order can't be over 64.  No
machine has inefficient access to bytes since EV5, and while those are
still supported, we don't optimise for them any more.  This does not
shrink struct page, but it removes an ifdef and frees up 2-6 bytes for
future use.

diff of pahole output:

 		struct callback_head callback_head;      /*    32    16 */
 		struct {
 			long unsigned int compound_head; /*    32     8 */
-			unsigned int compound_dtor;      /*    40     4 */
-			unsigned int compound_order;     /*    44     4 */
+			unsigned char compound_dtor;     /*    40     1 */
+			unsigned char compound_order;    /*    41     1 */
 		};                                       /*    32    16 */
 	};                                               /*    32    16 */
 	union {

[[email protected]: add comment]
  Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Randy Dunlap <[email protected]>
Signed-off-by: Matthew Wilcox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions