Using eager strategies to improve NFS I/O performance

Abstract

Typical network file system (NFS) clients write lazily: they leave dirty pages in the page cache and defer writing to the server. This reduces network traffic when applications repeatedly modify the same set of pages. However, this approach can lead to memory pressure, when the number of available pages on the client system is so low that the system must work harder to reclaim dirty pages. We show that NFS performance is poor under memory pressure and present two mechanisms to solve it: eager writeback and eager page laundering. These mechanisms change the client's data management policy from lazy to eager, in which dirty pages are written back proactively, resulting in higher throughput for sequential writes. In addition, we show that NFS servers suffer from out-of-order file operations, which further reduce performance. We introduce request ordering, a server mechanism to process operations, as much as possible, in the order they were sent by the client, which improves read performance substantially. We have implemented these techniques in the Linux operating system. I/O performance is improved, with the most pronounced improvement visible for sequential access to large files. We see 33% improvement in the performance of streaming write workloads and more than triple the performance of streaming read workloads. We evaluate several non-sequential workloads and show that these techniques do not degrade performance, and can sometimes improve performance.