Abstract
Virtualization is widely used in modern computer systems ranging from personal computers to cloud servers as it provides various heterogeneous platforms at low cost. However, due to its nested software structure in host and guest machines that are difficult to harmonize, it is challenging to manage resources efficiently in virtualized systems. In this article, we anatomize the overhead of virtualization associated with file system journaling and discover the excessively frequent commits that take place in virtualized systems. This is because the host triggers commit on every write request from all guest machines. This also generates unnecessary write traffic to storage. To remedy these problems, we propose the VM-separated commit, and implement it on QEMU-KVM and Ext4. Specifically, we devise a data structure that manages modified file blocks from each guest as a separate list and split the running transaction list into two sub-transactions based on this data structure upon a commit request from a guest. Measurement studies with Filebench and IOzone benchmarks show that the proposed policy improves the I/O throughput by 19.5% on average and up to 64.2% over existing systems. It also reduces the variability in performance.
Highlights
Virtualization techniques are widely used in various modern computer systems ranging from personal computers to cloud servers [1,2,3,4,5,6]
It reduces the variability in performance
Though our evaluation study is performed on KVM and Ext4, it is noted that the observations that we make and the policy that we propose are applicable to any platform that makes use of full virtualization and transaction-based file systems
Summary
Virtualization techniques are widely used in various modern computer systems ranging from personal computers to cloud servers [1,2,3,4,5,6]. The frequent commits generate a significant amount of unnecessary write traffic to storage as file systems such as Ext, Btrfs, and ZFS, manage all modified file blocks through a single transaction list. We observe that this unnecessary I/O traffic constitutes 43% on average and up to 63% of the total write traffic. Though our evaluation study is performed on KVM and Ext, it is noted that the observations that we make and the policy that we propose are applicable to any platform that makes use of full virtualization and transaction-based file systems (e.g., journaling file systems or copy-on-write file systems).
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