Puma: pooling unused memory in virtual machines for I/O intensive applications

International audienceWith the advent of cloud architectures, virtualization has become a key mechanism. In clouds, virtual machines (VMs) offer both isolation and flexibility. This is the foundation of cloud elasticity, but it induces fragmentation of the physical resources, including memory. While each VM memory needs evolve during time, existing mechanisms used to dynamically adjust VMs memory are inefficient, and it is currently impossible to take benefit of the unused memory of VMs hosted by another host. In this paper we propose Puma, a mechanism that improves I/O intensive applications performance by providing the ability for a VM to entrust clean page-cache pages to other VMs having unsused memory. By reusing the existing page-cache data structures, Puma is very efficient to reclaim the memory lent to another VM. By being distributed, Puma increases the memory consolidation at the scale of a data center. In our evaluations made with TPC-C, TPC-H, BLAST and Postmark, we show that Puma can significantly boost the performance without impacting potential activity peaks on the lender