On linux the code cache cannot be mapped using large pages because linux shared memory does not allow executable permissions to be set.  From the shmget man page:

       ...
       mode_flags (lowest 9 bits)
                   specifying  the  permissions  granted to the owner, group,
                   and world.  Presently, the  execute  permissions  are  not
                   used by the system.

If/when linux shared mem supports execute permission, or if/when linux gets another method of obtaining large page memory, the JVM should map the code cache with large pages.