Increasing the Transparent Page Sharing in Java

Improving memory utilization is important for improving the efficiency of a cloud datacenter by increasing the number of usable VMs. Memory over-commitment is a common technique for this purpose. Transparent Page Sharing (TPS) is a technique to improve the utilization by sharing identical memory pages to reduce the total memory consumption. For a cloud datacenter, we might expect TPS will reduce memory usage because VMs often execute the same OS and middleware and thus they may have many identical pages. However, TPS is less effective for Java-based middleware because the Java VM finds it difficult to manage the layouts of internal data structures that depend on the execution of Java programs. This paper presents detailed breakdowns of the memory usage of KVM guest VMs executing a Java-based Web application server. Then we propose increasing the amount of page sharing by utilizing a class sharing mechanism in the Java VM. Our approach reduced the measured physical memory for class metadata by up to 89.6% when using the Apache DayTrader benchmark running on four guest VMs in a KVM host machine.