Memory usage increase in WSO2 GREG

By extending the wso2 GREG i have designed a storage server with saves the metadata to database and binary data to a file server with user registry implementation used in the WSO2 GREG. For data storage i used a backend web service access the data layer of my application. Both download upload function works fine. However each time i make a request for either upload or download the RAM usage on the host server increases. For java heap arguments are this: -Xms1024m -Xmx8192m -XX:MaxPermSize=256m (My host has RAM of 8GB). I am using WSO2 GREG 4.0.0 . What can be the cause of the memory consumption increase? Thanks in advance