mm: save some bytes in mm_struct by filling holes on 64bit

Save some bytes in mm_struct by filling holes

Putting int values together for better packing on 64bit shrinks sizeof(struct
mm_struct) from 776 bytes to 764 bytes.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>