The Case for Replication-Aware Memory-Error Protection in Disaggregated Memory

Disaggregated memory leverages recent technology advances in high-density, byte-addressable non-volatile memory and high-performance interconnects to provide a large memory pool shared across multiple compute nodes. Due to higher memory density, memory errors may become more frequent. Unfortunately, tolerating memory errors through existing memory-error protection techniques becomes impractical due to increasing storage cost. This work proposes replication-aware memory-error protection to improve storage efficiency of protection in data-centric applications that already rely on memory replication for performance and availability. It lets such applications lower protection storage cost by weakening the protection of each individual replica, but still realize a strong protection target by relying on the collective protection conferred by multiple replicas

SplitFS: Reducing Software Overhead in File Systems for Persistent Memory

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 4x compared to the NOVA PM file system, and 17x 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 2x compared to ext4 DAX and NOVA while providing similar consistency guarantees

Virtual Machine Support for Many-Core Architectures: Decoupling Abstract from Concrete Concurrency Models

The upcoming many-core architectures require software developers to exploit concurrency to utilize available computational power. Today's high-level language virtual machines (VMs), which are a cornerstone of software development, do not provide sufficient abstraction for concurrency concepts. We analyze concrete and abstract concurrency models and identify the challenges they impose for VMs. To provide sufficient concurrency support in VMs, we propose to integrate concurrency operations into VM instruction sets. Since there will always be VMs optimized for special purposes, our goal is to develop a methodology to design instruction sets with concurrency support. Therefore, we also propose a list of trade-offs that have to be investigated to advise the design of such instruction sets. As a first experiment, we implemented one instruction set extension for shared memory and one for non-shared memory concurrency. From our experimental results, we derived a list of requirements for a full-grown experimental environment for further research

Pathological Interaction of Locks with Transactional Memory

Transactional memory (TM) promises to simplify multithreaded programming. Transactions provide mutual exclusion without the possibility of deadlock and the need to assign locks to data structures. To date, most investigations of transactional memory have looked at purely transactional systems that do not interact with legacy code using locks. Unfortunately, the reality of software engineering is that such interaction is likely. We investigate the interaction of transactional memory implementations and lock-based code. We identify and discuss five pathologies that arise with different systems when a lock is accessed both within and outside a transaction: Blocking, Deadlock, Livelock, Early Release, and Invisible Locking. To address these pathologies we designed and implemented transaction-safe locks (TxLocks) by modifying the existing lock implementation of the OpenSolaris C Library and extending the conflict resolution policy of a hardware transactional memory system

Latency Prediction for Delay-sensitive V2X Applications in Mobile Cloud/Edge Computing Systems

Mobile edge computing (MEC) is a key enabler of delay-sensitive vehicle-to-everything (V2X) applications. Determining where to execute a task necessitates accurate estimation of the offloading latency. In this paper, we propose a latency prediction framework that integrates machine learning and statistical approaches. Aided by extensive latency measurements collected during driving, we first preprocess the data and divide it into two components: one that follows a trackable trend over time and the other that behaves like random noise. We then develop a Long Short-Term Memory (LSTM) network to predict the first component. This LSTM network captures the trend in latency over time. We further enhance the prediction accuracy of this technique by employing a k-medoids classification method. For the second component, we propose a statistical approach using a combination of Epanechnikov Kernel and moving average functions. Experimental results show that the proposed prediction approach reduces the prediction error to half of a standard deviation (STD) of the raw data. © 2020 IEEE.National Science FoundationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]