EROFS: A Compression-friendly Readonly File System for Resource-scarce Devices

Smartphones usually have limited storage and runtime memory. Compressed read-only file systems can dramatically decrease the storage used by read-only system resources. However, existing compressed read-only file systems use fixed-sized input compression, which causes significant I/O amplification and unnecessary computation. They also consume excessive runtime memory during decompression and deteriorate the performance when the runtime memory is scarce. In this paper, we describe EROFS, a new compression-friendly read-only file system that leverages fixed-sized output compression and memory-efficient decompression to achieve high performance with little extra memory overhead. We also report our experience of deploying EROFS on tens of millions of smartphones. Evaluation results show that EROFS outperforms existing compressed read-only file systems with various micro-benchmarks and reduces the boot time of real-world applications by up to 22.9% while nearly halving the storage usage.