Memory Usage issue on a Linux Server with DB2 LUW database installed

We have Linux server with DB2 LUW database installed on it. Total memory allocated for the server is 256 GB, out of which 234 GB was allocated to the database. Daatabase has the automatic memory enabled, current allocation is 234 GB. When i checked in the server, the free memory avaialble is only 345 MB. Where as in the app manager, Memory utilization is showing only 1%. When 234 GB out of 256 GB is allocated to database in the server, why the server memory utilization is showing as only 1% used. It is misleading us when we want to configure alerts for the Memory utilization threshold... Please help me to understand how memory usage is being monitored for Linux server in app manager.