Linux high memory utilization

Today I was working on a project when the tester said the memory utilization was close to 100% always.First I was surprised as this was a pure DB box (RH 4) and has a single instance using only 50% of the memory for the Db.

As usual the first thing I did was to check the TOP/vmstat command, but this does not give the correct picture as Linux uses the spare memory available for caching the disk blocks (yes might be useful for a slow storage - extra cache) which is also accounted in the TOP command.


TOP:

Mem: 49433916k total, 47201932k used, 2231984k free, 903556k buffers
Swap: 70894792k total, 4k used, 70894788k free, 22948700k cached

VMSTAT:

vmstat 2 4
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
r b swpd free buff cache si so bi bo in cs us sy id wa st
1 3 4 2250296 903688 22950204 0 0 1149 38 1 0 1 1 95 3 0
1 4 4 2249804 903688 22950204 0 0 39225 27 13506 35171 3 2 86 10 0
1 3 4 2250604 903688 22950204 0 0 42305 61 14293 35447 3 2 85 11 0
0 3 4 2250836 903688 22950204 0 0 29921 96 10224 25105 3 1 85 11 0



So in Linux we have to read the cached value carefully to calculate the actual memory used or the easier way is to cuse the free -m command as below.Here 22795 is the actual memory used and 25479 is the free memory.


free -m
total used free shared buffers cached
Mem: 48275 46090 2185 0 882 22412
-/+ buffers/cache: 22795 25479
Swap: 69233 0 69233