zIO: Accelerating IO-Intensive Applications with Transparent Zero-Copy IO

We present zIO, a transparent zero-copy IO mechanism for unmodified IO-intensive applications. zIO tracks IO data through the application, eliminating copies that are unnecessary while maintaining data consistency.

Applications often modify only a part of the data they process. zIO leverages this insight and interposes on IO stack and standard library memory copy calls to track IO data and eliminate unnecessary copies. Instead, intermediate data locations are unmapped, allowing zIO to intercept and resolve any access via page faults to maintain data consistency. To avoid harming application performance in situations where data tracking overhead is high, zIO's tracking policy decides on a per IO basis when to eliminate copies. Further, we demonstrate how to use zIO to achieve optimistic network receiver persistence for applications storing data from the network in non-volatile memory (NVM). By mapping socket receive buffers in NVM and leveraging kernel-bypass IO, we can rely on zIO to transparently eliminate all copies from the network, through the application, to storage.

We implement zIO as a user-space library. On top of kernel IO stacks, zIO eliminates application-level IO copies. We also integrate zIO with kernel-bypass IO stacks, where it can additionally eliminate copies incurred by the IO stack APIs and enable optimistic network receiver persistence. We evaluate zIO with IO-intensive applications, such as Redis, Icecast, and MongoDB. zIO improves application throughput by up to 1.8× with Linux and by up to 2.5× with kernel-bypass IO stacks and optimistic network receiver persistence. Compared to common uses of zero-copy IO stack APIs, such as memory mapped files, zIO can improve performance by up to 17% due to reduced TLB shootdown overhead.