User-Space Process Virtualization in the Context of Checkpoint-Restart and Virtual Machines

TLDR: This dissertation presents user-space process virtualization to decouple application processes from the external subsystems and an adaptive plugin based approach is used to implement the virtualization layers that allow the checkpoint-restart system to grow organically.

Abstract: Checkpoint-Restart is the ability to save a set of running processes to a checkpoint image on disk, and to later restart them from the disk. In addition to its traditional use in fault tolerance, recovering from a system failure, it has numerous other uses, such as for application debugging and save/restore of the workspace of an interactive problem-solving environment. Transparent checkpointing operates without modifying the underlying application program, but it implicitly relies on a “Closed World Assumption” — the world (including file system, network, etc.) will look the same upon restart as it did at the time of checkpoint. This is not valid for more complex programs. Until now, checkpoint-restart packages have adopted ad hoc solutions for each case where the environment changes upon restart. This dissertation presents user-space process virtualization to decouple application processes from the external subsystems. A thin virtualization layer is introduced between the application and each external subsystem. It provides the application with a consistent view of the external world and allows for checkpoint-restart to succeed. The ever growing number of external subsystems make it harder to deploy and maintain virtualization layers in a monolithic checkpoint-restart system. To address this, an adaptive plugin based approach is used to implement the virtualization layers that allow the checkpoint-restart system to grow organically. The principle of decoupling the external subsystem through process virtualization is also applied in the context of virtual machines for providing a solution to the long standing double-paging problem. Double-paging occurs when the guest attempts to page out memory that has previously been swapped out by the hypervisor and leads to long delays for the guest as the contents are read back into machine memory only to be written out again. The performance rapidly drops as a result of significant lengthening of the time to complete the guest I/O request.