SNMP OID for Total Memory Used.

I have the OID for total memory which is: Name/OID: sysHostMemoryTotalKb.0; Value (Gauge): 8189780

 

What is the OID for the total memory used?:

 

It appears that sysHostMemoryUsedKb is not: Name/OID: sysHostMemoryUsedKb.0; Value (Gauge): 3863145

 

As when I do top I get different values:

 

Mem: 8189780k total, 8089472k used, 100308k free, 469308k buffers

 

Total memory value matches with top which tell me I am almost close.

 

I am asking this because I want to graph a memory usage on my system monitoring tool.

 

Please advise,

 

Thanks, Edouard,.