sysctl -zarc for ZFS users

[Yoshihiro Ota]

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 @
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