Efficient Memory Overcommitment for I/O Passthrough Enabled VMs via Fine-grained Page Meta-data Management


Yaohui Wang, Ben Luo, and Yibin Shen, Alibaba Group


In virtualization systems, guest memory overcommitment helps to improve the utilization of the host memory resource. However, the widely adopted I/O passthrough technique makes this task not intuitive since the hypervisor must avoid DMA (Direct Memory Access) failures when the I/O device accesses the guest memory. There already exist several solutions, for example, IOPF (I/O Page Fault) can fix DMA failures by allowing page fault triggered from the I/O device side, vIOMMU and coIOMMU avoid DMA failures by monitoring the DMA buffers in the guest. However, these solutions all face the performance concerns introduced by the memory backup/restore mechanism, i.e., memory swapping. Some free page based methods (e.g., Ballooning, Free Page Reporting, Hyperupcall) are free from memory swapping, but they either are not DMA-safe or introduce high guest communication overhead. In this paper, we propose V-Probe, a high-efficiency approach to achieve memory overcommitment for I/O passthrough enabled VMs. Using fine-grained page meta-data management, V-Probe allows the hypervisor to inspect and reclaim guest free pages actively and efficiently while guaranteeing DMA-safety. Experiments show that, for both memory reclamation and reallocation, the overhead of V-Probe is in the scale of microseconds, which is faster than Ballooning and IOPF based methods by two orders of magnitude. And our micro-benchmark and macro-benchmark show that V-Probe limits the performance impact of memory overcommitment to a low level.

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@inproceedings {288776,
author = {Yaohui Wang and Ben Luo and Yibin Shen},
title = {Efficient Memory Overcommitment for {I/O} Passthrough Enabled {VMs} via Fine-grained Page Meta-data Management},
booktitle = {2023 USENIX Annual Technical Conference (USENIX ATC 23)},
year = {2023},
isbn = {978-1-939133-35-9},
address = {Boston, MA},
pages = {769--783},
url = {https://www.usenix.org/conference/atc23/presentation/wang-yaohui},
publisher = {USENIX Association},
month = jul