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1. Rethinking File Mapping for Persistent Memory

   Neal, Ian; Zuo, Gefei; Shiple, Eric; Khan, Tanvir; Kwon, Youngjin; Peter, Simon; Kasikci, Baris (January 2021, 19th USENIX Conference on File and Storage Technologies (FAST 21))

   null (Ed.)

   Persistent main memory (PM) dramatically improves IO performance. We find that this results in file systems on PM spending as much as 70% of the IO path performing file mapping (mapping file offsets to physical locations on storage media) on real workloads. However, even PM-optimized file systems perform file mapping based on decades-old assumptions. It is now critical to revisit file mapping for PM. We explore the design space for PM file mapping by building and evaluating several file-mapping designs, including different data structure, caching, as well as meta-data and block allocation approaches, within the context of a PM-optimized file system. Based on our findings, we design HashFS, a hash-based file mapping approach. HashFS uses a single hash operation for all mapping and allocation operations, bypassing the file system cache, instead prefetching mappings via SIMD parallelism and caching translations explicitly. HashFS’s resulting low latency provides superior performance compared to alternatives. HashFS increases the throughput of YCSB on LevelDB by up to 45% over page-cached extent trees in the state-of-the-art Strata PM-optimized file system 

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2. SplitFS: Reducing Software Overhead in File Systems for Persistent Memory

   https://doi.org/10.1145/3341301.3359631  

   Rohan Kadekodi, Se Kwon (October 2020, Proceedings of the 27th ACM Symposium on Operating Systems Principles)

   We present SplitFS, a file system for persistent memory (PM) that reduces software overhead significantly compared to state-of-the-art PM file systems. SplitFS presents a novel split of responsibilities between a user-space library file system and an existing kernel PM file system. The user-space library file system handles data operations by intercepting POSIX calls, memory-mapping the underlying file, and serving the read and overwrites using processor loads and stores. Metadata operations are handled by the kernel PM file system (ext4 DAX). SplitFS introduces a new primitive termed relink to efficiently support file appends and atomic data operations. SplitFS provides three consistency modes, which different applications can choose from, without interfering with each other. SplitFS reduces software overhead by up-to 4× compared to the NOVA PM file system, and 17× compared to ext4 DAX. On a number of micro-benchmarks and applications such as the LevelDB key-value store running the YCSB benchmark, SplitFS increases application performance by up to 2× compared to ext4 DAX and NOVA while providing similar consistency guarantees. 

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3. A quantum processor based on coherent transport of entangled atom arrays

   https://doi.org/10.1038/s41586-022-04592-6  

   Bluvstein, Dolev; Levine, Harry; Semeghini, Giulia; Wang, Tout T.; Ebadi, Sepehr; Kalinowski, Marcin; Keesling, Alexander; Maskara, Nishad; Pichler, Hannes; Greiner, Markus; et al (April 2022, Nature)

   Abstract The ability to engineer parallel, programmable operations between desired qubits within a quantum processor is key for building scalable quantum information systems 1,2 . In most state-of-the-art approaches, qubits interact locally, constrained by the connectivity associated with their fixed spatial layout. Here we demonstrate a quantum processor with dynamic, non-local connectivity, in which entangled qubits are coherently transported in a highly parallel manner across two spatial dimensions, between layers of single- and two-qubit operations. Our approach makes use of neutral atom arrays trapped and transported by optical tweezers; hyperfine states are used for robust quantum information storage, and excitation into Rydberg states is used for entanglement generation 3–5 . We use this architecture to realize programmable generation of entangled graph states, such as cluster states and a seven-qubit Steane code state 6,7 . Furthermore, we shuttle entangled ancilla arrays to realize a surface code state with thirteen data and six ancillary qubits 8 and a toric code state on a torus with sixteen data and eight ancillary qubits 9 . Finally, we use this architecture to realize a hybrid analogue–digital evolution 2 and use it for measuring entanglement entropy in quantum simulations 10–12 , experimentally observing non-monotonic entanglement dynamics associated with quantum many-body scars 13,14 . Realizing a long-standing goal, these results provide a route towards scalable quantum processing and enable applications ranging from simulation to metrology. 

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4. Recipe: converting concurrent DRAM indexes to persistent-memory indexes

   https://doi.org/10.1145/3341301.3359635  

   Se Kwon Lee, Jayashree Mohan (October 2019, Proceedings of the 27th ACM Symposium on Operating Systems Principles)

   We present Recipe, a principled approach for converting concurrent DRAM indexes into crash-consistent indexes for persistent memory (PM). The main insight behind Recipe is that isolation provided by a certain class of concurrent in-memory indexes can be translated with small changes to crash-consistency when the same index is used in PM. We present a set of conditions that enable the identification of this class of DRAM indexes, and the actions to be taken to convert each index to be persistent. Based on these conditions and conversion actions, we modify five different DRAM indexes based on B+ trees, tries, radix trees, and hash tables to their crash-consistent PM counterparts. The effort involved in this conversion is minimal, requiring 30--200 lines of code. We evaluated the converted PM indexes on Intel DC Persistent Memory, and found that they outperform state-of-the-art, hand-crafted PM indexes in multi-threaded workloads by up-to 5.2x. For example, we built P-CLHT, our PM implementation of the CLHT hash table by modifying only 30 LOC. When running YCSB workloads, P-CLHT performs up to 2.4x better than Cacheline-Conscious Extendible Hashing (CCEH), the state-of-the-art PM hash table. 

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5. Interactive Visual Representation of Inter-Connected Requirements in Building Codes

   https://doi.org/10.1061/9780784483961.105  

   Xue, Xiaorui; Zhang, Jiansong; El-Gohary, Nora (March 2022, Construction Research Congress 2022)

   To facilitate a better understanding of building codes, the visualization of the embedded structures of the provisions and requirements of the codes is needed. Existing research efforts in building code compliance checking mostly do not purposefully represent building codes in formats that facilitate human understanding and interaction with the codes, such as XML and hypertext (text with links to other text). Visual programming commonly represents building codes more visually as flowcharts. However, flowcharts are static, and the generation of flowcharts is still manual. To address this lack of interactive visual representation of building code requirement structures, this paper proposes an automated building code structure extraction and visualization method for visualizing building code contents in a way that clearly shows the inter-connections between requirements and allows intuitive user interaction. In this method, to extract the chapter-section-subsection hierarchical structure and cross-reference structure, a new extraction method named Building Code Network Generator (BCNG) is proposed to automatically generate an interactive visualization using a directed network. The performance of the proposed BCNG was empirically tested on Chapters 5 and 10 of the International Building Code 2015, with a resulting precision, recall, and F1-score of 99.4%, 96.3%, and 97.8%, respectively. In addition, the extracted hierarchical and cross-reference structures were displayed using an open-source network visualization tool to facilitate human understanding and interactions with the building code requirements in automated compliance checking systems. 

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