ZFS uses more memory than allocated to it

Hi,

    We have restricted ZFS arc size in the /etc/system file to use upto 2 GB.

# cat /etc/system | tail -3
set zfs:zfs_arc_min = 536870912
set zfs:zfs_arc_max = 2147483648

When i check the ZFS usage, its more than 2 GB.

# echo ::memstat | mdb -k
Page Summary                Pages                MB  %Tot
------------     ----------------  ----------------  ----
Kernel                     367970              2874   18%
ZFS File Data              373462              2917   18%
Anon                       999842              7811   49%
Exec and libs               27026               211    1%
Page cache                  98307               768    5%
Free (cachelist)            34404               268    2%
Free (freelist)            156652              1223    8%

Total                     2057663             16075
Physical                  2038140             15922

Could you please explain why this is happening. Am i missing any other settings related to ZFS arc.

Thanks.