# Reconstruct the Directories for In-Memory File Systems

## TL;DR

This paper introduces Content-Indexed Browsing (CIB), a novel path lookup method for in-memory file systems on persistent memory, significantly improving lookup speed and reducing write overhead.

## Contribution

It proposes a new directory structure for fast, logarithmic-time path lookup in persistent memory file systems, and demonstrates its effectiveness through implementation and evaluation.

## Key findings

- CIB achieves $O(log(n))$ search time for directory lookups.
- CIB improves overall PMFS performance by 20.4%.
- CIB drastically reduces write operations on persistent memory.

## Abstract

Existing path lookup routines in file systems need to construct an auxiliary index in memory or traverse the dentries of the directory file sequentially, which brings either heavy writes or large timing cost. This paper designs a novel path lookup mechanism, Content-Indexed Browsing (CIB), for file systems on persistent memory, in which the structure of directory files is an exclusive index that can be searched in $O(log(n))$ time. We implement CIB in a real persistent memory file system, PMFS, denoted by CIB-PMFS. Comprehensive evaluations show that CIB can achieve times of performance improvement over the conventional lookup schemes in PMFS, and brings 20.4\% improvement on the overall performance of PMFS. Furthermore, CIB reduces the writes on persistent memory by orders of magnitude comparing with existing extra index schemes.