Towards Application-level I/O Proportionality with a Weight-aware Page Cache Management

Cloud systems often use blkio subsystem of Cgroups for controlling I/O resources to guarantee the service-level objective (SLO) of the systems. However, the blkio subsystem of Cgroups is originally designed to achieve block-level I/O proportionality without consideration on the upper layers of the system software stack, such as the page cache layer. Therefore, when an application utilizes buffered I/O, the performance of the application can exhibit unexpected results in its I/O proportionality even though the block-level I/O proportionality is still being guaranteed. To address this problem, we suggest a weight-aware page cache management scheme, called Justitia, which realizes application-level I/O proportionality in the systems that use OS virtualization technologies. Justitia prioritizes higher-weighted applications in the lock acquisition process of the page allocation by re-ordering the lock waiting queue based on their I/O weights. Additionally, it keeps the number of allocated pages for each application proportional to its I/O weight, with a weight-aware page reclamation scheme. Our experiments show that Justitia effectively improves I/O proportionality with negligible overhead in various cases.