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    Item type:Publication, Access status: with files ,
    Short paper: simulation-based performance characterization of common NOR flash file systems
    (Association for Computing Machinery (ACM), 2026-05)
    Loeck, Yannick
    ;
    Dietrich, Christian
    ;
    Kulau, Ulf
    NOR flash memory is widely used as storage in embedded systems as it offers dense non-volatile memory up to the gigabit range while being more reliable than NAND flash. To avoid the cost of a standalone flash controller in such small systems, specialized flash file systems are used to handle the limited write endurance and asymmetric program/erase characteristics. While many NOR file systems exist and are extensively deployed, there is a lack of systematic comparisons of their performance. In this paper, we present vflashsim, a simulator for capturing interactions between file systems and flash memory and for running representative benchmarks. Unlike evaluations on physical hardware, our simulation-based approach avoids prohibitively long erase latencies and cell wear. We implement a NOR flash model and, using vflashsim, evaluate four representative file systems, SPIFFS, LittleFS, YAFFS2, and NF2FS, in terms of write amplification, garbage-collection behavior, and RAM utilization. Our analysis shows how design choices and implementation bugs, such as excessive device scanning, unconditional sector erases, and a lack of garbage collection in allocation paths, cause substantial performance issues. Additionally, we identify how to provoke failure conditions in different file systems, which can result in unrecoverable crashes. Among the evaluated file systems, YAFFS demonstrates the best overall performance and reliability at the cost of high RAM usage, whereas a modified LittleFS remains the best option for more memory-constrained systems. Since performance trade-offs vary by workload and hardware constraints, no single file system is universally optimal. With vflashsim, we provide a tool that enables developers and users of flash file systems to analyze their behavior under diverse configurations and workloads.
    Publicationtype: Conference Paper
      20  13
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    Evaluation and refinement of an explicit virtual-memory primitive
    (IEEE, 2023)
    Loeck, Yannick
    ;
    Dietrich, Christian
    The general-purpose virtual-memory subsystem of Linux does not scale to the multimillion IOP/s SSDs of today. Further, its implicit write-back and back-fill semantic hinders data-intensive applications, like databases, more than it actually helps. In contrast, explicit virtual-memory abstractions, as introduced by ExMap, provide an Exokernel-like interface to manipulate theVMsurface. Thereby, the user application remains in full control over the VM surface and can benefit from low operation latencies. In this paper, we investigate the performance of the existing ExMap abstraction and propose enhancements for its system-call interface, its process-local memory pool management, and the user-space page-state tracking. With memory-mapped I/O vectors, the global bundle list, and exported page tables, we improve the end-toend throughput of in-memory random B+tree lookups by up to 5.7 percent, while the out-of-memory case improves by up to 4.9 percent.
    Publicationtype: Journal Article
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