Red HAT AS3 memory issues

[mac subbu]

HI,

We have a linux AS3 on a server with 4 GB RAM

At any point of time my Free -m  Gives total of 4000 mb and used of  3900
and free 10 mb  but my buffers/cache used is hardly 1000 mb and 3000 mb free

  Whereas

   the top always gives

  mem used 4000 mb avg and used 3972

  Going by bufffers/cache i shudnt be having memory issues BUT our server is
monitored and keeps throwing above 80% memory utilisation all the time


  why is there a discrepancy between TOP and FREE and which shud be used
more definitely for memory analysis

  and why do we get over 80% used all the time when buffers/cache is low all
times

Any pointers would be appreciated

regards