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.

Most database management systems cache pages from storage in a main memory buffer pool. To do this, they either rely on a hash table that translates page identifiers into pointers, or on pointer swizzling which avoids this translation. In this work, we propose vmcache, a buffer manager design that instead uses hardware-supported virtual memory to translate page identifiers to virtual memory addresses. In contrast to existing mmap-based approaches, the DBMS retains control over page faulting and eviction. Our design is portable across modern operating systems, supports arbitrary graph data, enables variable-sized pages, and is easy to implement. One downside of relying on virtual memory is that with fast storage devices the existing operating system primitives for manipulating the page table can become a performance bottleneck. As a second contribution, we therefore propose exmap, which implements scalable page table manipulation on Linux. Together, vmcache and exmap provide flexible, efficient, and scalable buffer management on multi-core CPUs and fast storage devices.