Recent research efforts propose remote memory systems that pool memory from multiple hosts. These systems rely on the virtual memory subsystem to track application memory accesses and transparently offer remote memory to applications. We outline several limitations of this approach, such as page fault overheads and dirty data amplification. Instead, we argue for a fundamentally different approach: leverage the local host's cache coherence traffic to track application memory accesses at cache line granularity. Our approach uses emerging cache-coherent FPGAs to expose cache coherence events to the operating system. This approach not only accelerates remote memory systems by reducing dirty data amplification and by eliminating page faults, but also enables other use cases, such as live virtual machine migration, unified virtual memory, security and code analysis. All of these use cases open up many promising research directions.

As the latency of the network approaches that of memory, it becomes increasingly attractive for applications to use remote memory---random-access memory at another computer that is accessed using the virtual memory subsystem. This is an old idea whose time has come, in the age of fast networks. To work effectively, remote memory must address many technical challenges. In this paper, we enumerate these challenges, discuss their feasibility, explain how some of them are addressed by recent work, and indicate other promising ways to tackle them. Some challenges remain as open problems, while others deserve more study. In this paper, we hope to provide a broad research agenda around this topic, by proposing more problems than solutions.

Commodity operating systems entrusted with securing sensitive data are remarkably large and complex, and consequently, frequently prone to compromise. To address this limitation, we introduce a virtual-machine-based system called Overshadow that protects the privacy and integrity of application data, even in the event of a total OScompromise. Overshadow presents an application with a normal view of its resources, but the OS with an encrypted view. This allows the operating system to carry out the complex task of managing an application's resources, without allowing it to read or modify them. Thus, Overshadow offers a last line of defense for application data.Overshadow builds on multi-shadowing, a novel mechanism that presents different views of physical memory, depending on the context performing the access. This primitive offers an additional dimension of protection beyond the hierarchical protection domains implemented by traditional operating systems and processor architectures.We present the design and implementation of Overshadow and show how its new protection semantics can be integrated with existing systems. Our design has been fully implemented and used to protect a wide range of unmodified legacy applications running on an unmodified Linux operating system. We evaluate the performance of our implementation, demonstrating that this approach is practical.