High Memory Utilization at our portal systems

Hi Experts,

We have our SAP EP Portal system with NW 7.3. OS is HP UX 11 and DB is Oracle 11. We are using this EP Portal system only for ADS service currently. Portal systems are having physical memory 8 GB and swap memory 32 GB. It is showing 99% physical memory and 36% of swap memory is occupying always. If we stop the SAP Service then it is showing 40 percent usage. See the glance output screenshot at below:

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What can be the main cause of it and how to resolve it? Can anybody help me ?

Thanks

Asad