Reducing Write Amplification for Inodes of Journaling File System using Persistent Memory

Conventional journaling file systems, such as Ext4, guarantee data consistency by writing in-memory dirty inodes to block devices twice. The write back of inodes may contain up to 80% clean inode that is unnecessary to be written back, which caused severe write amplification problem and largely reduce performance since the size of an inode is several times less than the size of a basic unit for updating the block device. Emerging persistent memories (PMs), such as phase change memory, provide the possibility for storing the offset of inodes in memory persistently. In this paper, we propose an efficient scheme, Updating Frequency based Inode Aggregation (UFIA), to reduce the write amplification of dirty inodes using PM. The main idea of UFIA is to identify the frequently-updated inodes and reorganize them in adjacent physical locations on block device. Firstly, UFIA adopts PM as an inode mapping table for remapping logical inodes to any physical inodes. Secondly, we design an efficient algorithm for UFIA to identify and reorganize the frequently-updated inodes. We implement UFIA and integrate it into Ext4 (denoted by UFIA-Ext4) in Linux kernel 4.4.4. The experiments are conducted with widely-used benchmark Filebench. Compared with original Ext4, the experimental results show that UFIA significantly reduces the write amplification of inodes and improves 54% of the performance on average.