mm/swap_state.c: declare a few variables as __read_mostly

These global variables are only set during initialization or rarely
change, so declare them as __read_mostly.

Change-Id: Iefa78448381eae5bb0e08eb7a5e0e61cc251a4b3
Link: http://lkml.kernel.org/r/1507802349-5554-1-git-send-email-changbin.du@intel.com


Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 783cb68ee2d25d621326366c0b615bf2ccf3b402
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>