sysctl -zarc for ZFS users

Hi all.

I've been watching ZFS activites on my machine and
improved systat to monitor such.

One of my first goals is to watch ZFS cache statistics.

I posted my patch to the bugzilla _at_
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=195460
I've been using on 11-CURRENT and 10.1-RELEASE myself.

Regards,
Hiro

% systat -zarc
                       Total     MFU     MRU    Anon     Hdr   L2Hdr   Other
     ZFS ARC            206M     63M    136M    826K   1102K      0K   5251K

                                rate    hits  misses   total hits total misses
     arcstats                  : 75%    1183     388        23721         4202
     arcstats.demand_data      :  0%       0       0          528            0
     arcstats.demand_metadata  : 76%    1007     308        21441         2757
     arcstats.prefetch_data    :  0%       0       0            0            0
     arcstats.prefetch_metadata: 68%     176      80         1752         1445
     zfetchstats               : 44%     954    1204        26410        25482
     arcstats.l2               :  0%       0       0            0            0
     vdev_cache_stats          :  0%       0       0            0            0