may be you can use
sar -r 2 100 ( 2 is inteval time and 100 is polling number)
you must see like this
10:10:40 freemem freeswap
10:10:42
54903 4945408
10:10:44 54903 4945408
the result show you in pages , that mean now this system has freemem 54903 pages
if you want to calculate it to kbyte you use command
pagesize
that will show you like this
root@sol9_e250 # pagesize
8192
that mean 1 pagesize = 8k , if your system has 54903 pages , your system has freemem = (54903 *8)/1024 ~429 MB
+++++++++++++++++++++++
Second solution ( easy)
you use
vmstat 3 you shuold see like this
kthr memory
r b w swap free
0 0 0 2476904 447520
0 0 0 2473032 439552
0 0 0 2473032 439552
The memory tab , it shows
memory/swap: Free, unreserved swap space (Kb).
memory/free:
Free memory (Kb). (Note that this will grow until it reaches lotsfree, at which point the page scanner is started. See "Paging" for more details.) ( lotsfree is one parameter in kernel that you can set it by mdb -kw )
PS: Sorry about my weak english