Hi
I need to know the system performance :

 
# echo "::memstat" | mdb -k
Page Summary Pages MB %Tot
------------ ---------------- ---------------- ----
Kernel 358022 2797 9%
ZFS File Data 2427072 18961 59%
Anon 1096938 8569 27%
Exec and libs 12020 93 0%
Page cache 73859 577 2%
Free (cachelist) 52250 408 1%
Free (freelist) 81544 637 2%
Total 4101705 32044
Physical 4070935 31804

Check output of vmstat 1 . If you see high values in "sr" and "fr" columns, then you are facing memory shortage.

What you are seeing is most likely file system caching. Solaris considers unused memory a waste, so it parks (caches) data read from files or written to files in memory because it improves performance. The kernel will release file caches anytime there is a need for more memory.

Kernel 358022 2797 9%
ZFS File Data 2427072 18961 59%
Anon 1096938 8569 27%
Exec and libs 12020 93 0%
Page cache 73859 577 2%
Free (cachelist) 52250 408 1%
Free (freelist) 81544 637 2%
Total 4101705 32044
Physical 4070935 31804

Please edit your initial post with pasting the actual command output. That would make it much readable. There should be properly aligned columns here.
As you are asking, probably not. You might want to cap ZFS ARC size but that really depends on the applications you are running and their memory footprint.

Your can see "vmstat 1 5" output to determine the system performance.
ZFS will use physical memory as ARC cache unless until it used by application.
When application needs more memory ,ZFS will release the cache automatically.
So you really no need to worry about that.
From the below output,you just need to monitor r,b,w columns and sr column (scan rate).If these values quite more,then your system performance is degraded

bash-3.00# vmstat 1 5
 kthr      memory            page            disk          faults      cpu
 r b w   swap  free  re  mf pi po fr de sr f0 s0 s1 s2   in   sy   cs us sy id
 0 0 32 955436 35360 56 151  1  1  2  0 143 -0 4  0  0  486  666  340  1  2 97
 0 0 29 688464 24576  1  42  3  0  0  0  0  0  6  0  0  602  719  347  1  1 98
 0 0 29 688384 24544 580 672 0  0  0  0  0  0  0  0  0  589  767  312  0  4 95
 1 0 29 688384 24544  8   8  0  0  0  0  0  0  0  0  0  550  597  326  0  0 100
 0 0 29 688384 24544 242 709 0  0  0  0  0  0  0  0  0  610 20194 377  2  4 94
bash-3.00#