The non-volatile memory NVM has the illustrious merits of byte-addressability, fast speed, persistency and low power consumption, which make it attractive to be used as main memory. Commonly, user process dynamically acquires memory through memory allocators. However, traditional memory allocators designed with in-place data writes are not appropriate for non-volatile main memory NVRAM due to the limited endurance. For instance, the number of write operations is merely 10 8 times per PCM cell. In this paper, we quantitatively analyze the wear-oblivious of DRAM-oriented designed allocator-glibc malloc and the inefficiency of wearconscious allocator-NVMalloc. For example, the average imbalance factor (the maximum/the average) of memory allocation is about 7.5 and 3, respectively. Based on our observations, we propose WAlloc, an efficient wear-aware manual memory allocator designed for NVRAM, decouples metadata and data, uses Less Allocated First Out allocation policy and redirects the data writes. Experimental results show that the wear-leveling of WAlloc outperforms that of NVMalloc about 30% and 60% under random workloads and welldistributed workloads, respectively. In addition, considering the trade-off between space and wear-leveling, WAlloc reduces average data memory writes in 64 bytes block by average 1.5X comparing with malloc with almost 8% extra space overhead. Keywords-Non-Volatile Memory memory allocator wearaware I.978-1-4673-8590-9/15/$31.00 ©2015 IEEE

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The quick advances of Cloud and the advent of Fog computing impose more and more critical demand for computing and data transfer of low latency onto the underlying distributed computing infrastructure. Remote direct memory access (RDMA) technology has been widely applied for its low latency of remote data access. However, RDMA gives rise to a host of challenges in accelerating in-memory key–value stores, such as direct remote memory writes, making the remote system more vulnerable. This study presents an in-memory key–value system based on RDMA, named Craftscached, which enables: (1) buffering remote memory writes into a communication cache memory to eliminate direct remote memory writes to the data memory area; (2) dividing the communication cache memory into RDMA-writable and RDMA-readable memory zones to reduce the possibility of data corruption due to stray memory writes and caching data into an RDMA-readable memory zone to improve the remote memory read performance; and (3) adopting remote out-of-place direct memory write to achieve high performance of remote read and write. Experimental results in comparison with Memcached indicate that Craftscached provides a far better performance: (1) in the case of read-intensive workloads, the data access of Craftscached is about 7–43[Formula: see text] and 18–72.4% better than those of TCP/IP-based and RDMA-based Memcached, respectively; (2) the memory utilization of small objects is more efficient with only about 3.8% memory compaction overhead.

The non-volatile memory (NVM) has the merits of byte-addressability, fast speed, persistency and low power consumption, which make it attractive to be used as main memory. Commonly, user process dynamically acquires memory through memory allocators. However, traditional memory allocators designed with in-place data writes are not appropriate for the non-volatile main memory (NVRAM) due to the limited endurance. In this article, first, we quantitatively analyze the wear-oblivious of DRAM-oriented designed allocator—glibc malloc and the inefficiency of wear-conscious allocator NVMalloc. Then, we propose WAlloc, an efficient wear-aware manual memory allocator designed for NVRAM: (1) decouples metadata and data management; (2) distinguishes metadata with volatility; (3) redirects the data writes around to achieve wear-leveling; (4) redesigns an efficient and effective NVM copy mechanism, bypassing the CPU cache partially and prefetching data explicitly. Finally, experimental results show that the wear-leveling of WAlloc outperforms that of NVMalloc about 30% and 60% under random workloads and well-distributed workloads, respectively. Besides, WAlloc reduces the average data memory writes in 64 bytes block by 1.5 times comparing with glibc malloc. With the fulfillment of data persistency, cache bypassing NVM copy is better than cache line flushing NVM copy with performance improvement circa 14%.