File Defragmentation Scheme for a Log-Structured File System

Park, Jonggyu; Kang, Dong Hyun; Eom, Young Ik

doi:10.1145/2967360.2967622

Cited by 13 publications

(6 citation statements)

References 6 publications

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“…The previous work of AALFS [29] re-orders valid blocks based exclusively on the inode number. However, it cannot eliminate fragmentation in the case when the valid blocks randomly exist in terms of file offset.…”

Section: Related Work and Discussionmentioning

confidence: 99%

Anti-Aging LFS: Self-Defragmentation With Fragmentation-Aware Cleaning

Park

Eom

2020

IEEE Access

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For several decades, filesystem aging has been widely studied, but nonetheless, it still remains an unsolved problem. Among various filesystems, log-structured filesystems have been reported to be vulnerable to fragmentation due to their append-only write policy. Fragmentation hinders various I/O activities such as sequential read and trim operations, regardless of the underlying storage types. This paper extensively analyzes the rationale behind performance degradation incurred by fragmentation on various types of storage devices. To eliminate fragmentation without additional I/O overhead, we propose an antiaging log-structured filesystem, called AALFS. During segment cleaning, AALFS rearranges the order of valid blocks based on inode number and file offset to eliminate existing fragmentation. To enhance the efficacy of the reordering process, the new victim selection policy of AALFS reflects the fragmentation degree of each segment in the selection of victim segments. Our experimental results show that AALFS effectively eliminates fragmentation by up to 99.8% and significantly improves sequential read performance on various types of storage devices. Particularly, AALFS improves the sequential read throughput of IOzone on hard disk drives by up to 22.8 times.

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Section: Related Work and Discussionmentioning

confidence: 99%

Anti-Aging LFS: Self-Defragmentation With Fragmentation-Aware Cleaning

Park

Eom

2020

IEEE Access

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“…First, defragmentation is the most common method. Park et al proposed a file defragmentation scheme on log-structured file systems [50], addressing the severe fragmentation caused by log-structured methods to enhance sequential read performance on SSD. The scheme determines the fragmentation degree of every segments, and migrates the data in the highly fragmented segment to a new segment.…”

Section: Related Work a File Contiguitymentioning

confidence: 99%

CFFS: A Persistent Memory File System for Contiguous File Allocation With Fine-Grained Metadata

Liu

Wang

2022

IEEE Access

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Extensive research on persistent memory (PM)-aware file systems has led to the development of numerous methods for improving read/write throughput. In particular, accessing or modifying file contents in a similar manner to the memory operations through mmap is a common approach. We designed a file system, CFFS (Contiguous File Allocation with Fine-Grained Metadata File System), to rapidly allocate PM pages to upper layer applications for mmap and to alleviate page fault overheads due to mmap. We optimized the physical contiguity of files in PM to reduce file fragmentation and increase fragment alignment with the goal of reducing software overhead. To achieve this goal, we implemented greedybased buddy systems and implicit preallocation with a not-most-recently-used (NMRU) policy based on our overall page allocation strategy of considering not only the spatial but also the temporal locality of file access patterns. Furthermore, for efficient and atomic metadata operations, we fully leveraged the byte-addressable property of PM to design fine-grained metadata. CFFS adopts persistent doubly linked lists for directory operations to identify and recover from inconsistencies caused by system failures, doing so without using traditional log mechanisms. In experiments, CFFS showed superior page allocation performance to EXT4-DAX and NOVA did under different PM fragmentation levels. Our allocation algorithm also reduced the cost of page faults for frequently appended files. Finally, CFFS's lightweight directory operations performed excellently in creating and deleting files of various quantities. In summary, the main contribution of the paper is proposing an efficient page allocation algorithm to improve the performance of subsequent mmaps, based on the strategy of considering not only the spatial but also the temporal locality of file access patterns in PM file systems. Another contribution was the fine-grained and log-free method for atomic directory operations.

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“…There are a lot of valuable studies on how to improve the overall performance of computer systems [1][2][3][4][5][6][7][8][9][10][11][12]. For example, since the overall performance depends on the latency of input/output operations, many researchers in academia and industry have focused on hardware improvements (e.g., non-volatile memory, CXL, and NVMe SSD devices).…”

Section: Introductionmentioning

confidence: 99%

FragTracer: Real-Time Fragmentation Monitoring Tool for F2FS File System

Cho

Kang

2023

Sensors

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Emerging hardware devices (e.g., NVMe SSD, RISC-V, etc.) open new opportunities for improving the overall performance of computer systems. In addition, the applications try to fully utilize hardware resources to keep up with those improvements. However, these trends can cause significant file system overheads (i.e., fragmentation issues). In this paper, we first study the reason for the fragmentation issues on an F2FS file system and present a new tool, called FragTracer, which helps to analyze the ratio of fragmentation in real-time. For user-friendly usage, we designed FragTracer with three main modules, monitoring, pre-processing, and visualization, which automatically runs without any user intervention. We also optimized FragTracer in terms of performance to hide its overhead in tracking and analyzing fragmentation issues on-the-fly. We evaluated FragTracer with three real-world databases on the F2FS file system, so as to study the fragmentation characteristics caused by databases, and we compared the overhead of FragTracer. Our evaluation results clearly show that the overhead of FragTracer is negligible when running on commodity computing environments.

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File Defragmentation Scheme for a Log-Structured File System

Cited by 13 publications

References 6 publications

Anti-Aging LFS: Self-Defragmentation With Fragmentation-Aware Cleaning

Anti-Aging LFS: Self-Defragmentation With Fragmentation-Aware Cleaning

CFFS: A Persistent Memory File System for Contiguous File Allocation With Fine-Grained Metadata

FragTracer: Real-Time Fragmentation Monitoring Tool for F2FS File System

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