This thesis evaluates the feasibility of doing page sharing between virtual machines. To do this evaluation we proposed two different designs: One that is transparent to the guest operating system and a paravirtualized one. We implemented one of these based on Potemkin, which is a modification of the Xen virtual machine monitor. In this we find pages eligible for sharing by use of a technique called content-based page sharing. When identical pages are found, the actual sharing of pages is obtained using shadow page tables and Copy-on-Write. Finally the implementation was evaluated and we found no significant overheads except for the use of shadow page tables. The paravirtualized design should mitigate this overhead.
As for the feasibility of page sharing, we carried out a series of experiments. These explored sharing under good and bad conditions as well as under synthetic workloads. We concluded that page sharing is feasible and that most workloads that have similar kernels and applications have something to share.
Keywords: VM, VMM, hypervisor, Xen, Potemkin, VMware ESX Server, virtualization, paravirtualization, memory sharing, overcommitment, flash cloning, content-based page sharing, compare-by-hash, SFH, Copy-on-Write, COW, shadow page tables, ballooning, reverse mapping, zero pages, benchmarks.