COSMOS: Coordinated Management of Cores, Memory, and Compressed Memory Swap for QoS-Aware and Efficient Workload Consolidation for Memory-Intensive Applications

With the rapid growth in memory demands, the slowdown of DRAM scaling, and the DRAM price fluctuations, DRAM has become one of the critical resources in cloud computing systems and datacenters. The compressed memory swap (CMS) is a promising technique that improves the effective memory capacity of the underlying computer system by compressing and storing a subset of pages in memory instead of the disk swap. While prior works have extensively investigated resource management techniques for workload consolidation, they lack the capability of dynamically allocating cores, memory, and CMS to the consolidated applications in a controlled and efficient manner. To bridge this gap, this work presents the in-depth characterization of the impact of cores, memory, and CMS on the QoS and throughput of the consolidated latency-critical (LC) and batch applications. Guided by the characterization results, we propose COSMOS, a software-based runtime system for coordinated management of cores, memory, and CMS for QoS-aware and efficient workload consolidation for memory-intensive applications. COSMOS dynamically collects the runtime data from the consolidated applications and the underlying system and allocates the resources to the consolidated applications in a way that achieves high throughput with strong QoS guarantees. Our quantitative evaluation based on a real system and widely-used memory-intensive benchmarks demonstrates the effectiveness of COSMOS in that it robustly satisfies the QoS and achieves high throughput across all the evaluated workload mixes and scenarios and significantly reduces the number of explored system states

Conversion between Metavalent and Covalent Bond in Metastable Superlattices Composed of 2D and 3D Sublayers

Reversible conversion over multimillion times in bond types between metavalent and covalent bonds becomes one of the most promising bases for universal memory. As the conversions have been found in metastable states, an extended category of crystal structures from stable states via redistribution of vacancies, research on kinetic behavior of the vacancies is highly in demand. However, it remains lacking due to difficulties with experimental analysis. Herein, the direct observation of the evolution of chemical states of vacancies clarifies the behavior by combining analysis on charge density distribution, electrical conductivity, and crystal structures. Site-switching of vacancies of Sb2Te3 gradually occurs with diverged energy barriers owing to their own activation code: the accumulation of vacancies triggers spontaneous gliding along atomic planes to relieve electrostatic repulsion. Studies on the behavior can be further applied to multiphase superlattices composed of Sb2Te3 (2D) and GeTe (3D) sublayers, which represent superior memory performances, but their operating mechanisms were still under debate due to their complexity. The site-switching is favorable (suppressed) when Te–Te bonds are formed as physisorption (chemisorption) over the interface between Sb2Te3 (2D) and GeTe (3D) sublayers driven by configurational entropic gain (electrostatic enthalpic loss). Depending on the type of interfaces between sublayers, phases of the superlattices are classified into metastable and stable states, where the conversion could only be achieved in the metastable state. From this comprehensive understanding on the operating mechanism via kinetic behaviors of vacancies and the metastability, further studies toward vacancy engineering are expected in versatile materials