While scientific applications show increasing demand for memory speed and capacity, the performance gap between compute cores and the memory subsystem continues to spread. In response, heterogeneous memory systems integrating high-bandwidth memory (HBM) and non-volatile memory (NVM) alongside traditional DRAM on the CPU side are gaining traction. Despite the potential benefits of optimized memory selection for improved performance and efficiency, adapting applications to leverage diverse memory types often requires extensive modifications. Moreover, applications often comprise multiple execution phases with varying data access patterns. Since the capacity of the “fastest” memory is limited, relying solely on fixed data placement decisions may not yield optimal performance. Thus, considering allocation lifetimes and dynamically migrating data between memory types becomes imperative to ensure that performance-critical data for each phase resides in fast memory. To address these challenges, we developed a workflow incorporating memory access profiling, optimization techniques and a runtime system, which selects initial data placement for allocations and performs data migration during execution, considering the platform's memory subsystem characteristics and capacities. We formalize the optimization problems for initial and phase-based data placement and propose heuristics derived from memory profiling metrics to solve it. Additionally, we outline the implementation of these approaches, including allocation interception to enforce placement decisions. Experiments conducted with several applications on an Intel Ice Lake$(\text{DRAM}+\text{NVM})$and Sapphire Rapids$(\text{HBM}+\text{DRAM})$system demonstrate that our methodology can effectively bridge the performance gap between slow and fast memory in heterogeneous memory environments.

Over the past decades, the performance gap between the memory subsystem and compute capabilities continued to spread. However, scientific applications and simulations show increasing demand for both memory speed and capacity. To tackle these demands, new technologies such as high-bandwidth memory (HBM) or non-volatile memory (NVM) emerged, which are usually combined with classical DRAM. The resulting architecture is a heterogeneous memory system in which no single memory is “best”. HBM is smaller but offers higher bandwidth than DRAM, whereas NVM provides larger capacity than DRAM at a reasonable cost and less energy consumption. Despite that, in several cases, DRAM still offers the best latency out of all three technologies. In order to use different kinds of memory, applications typically have to be modified to a great extent. Consequently, vendor-agnostic solutions are desirable. First, they should offer the functionality to identify kinds of memory, and second, to allocate data on it. In addition, because memory capacities may be limited, decisions about data placement regarding the different memory kinds have to be made. Finally, in making these decisions, changes over time in data that is accessed, and the actual access pattern, should be considered for initial data placement and be respected in data migration at run-time. In this paper, we introduce a new methodology that aims to provide portable tools and methods for managing data placement in systems with heterogeneous memory. Our approach allows programmers to provide traits (hints) for allocations that describe how data is used and accessed. Combined with characteristics of the platforms’ memory subsystem, these traits are exploited by heuristics to decide where to place data items. We also discuss methodologies for analyzing and identifying memory access characteristics of existing applications, and for recommending allocation traits. In our evaluation, we conduct experiments with several kernels and two proxy applications on Intel Knights Landing (HBM + DRAM) and Intel Ice Lake with Intel Optane DC Persistent Memory (DRAM + NVM) systems. We demonstrate that our methodology can bridge the performance gap between slow and fast memory by applying heuristics for initial data placement.

For the past years, scientific applications and simulations show increasing demand for both memory speed and capacity. The performance gap between compute units and the memory subsystem continues to spread which led to redesigns and the emergence of new technologies. Recent architectures already comprise, next to classical DRAM, portions of High Bandwidth Memory (HBM) that has less capacity than DRAM and is solving only one of the requirements. The newly introduced Non- Volatile Memory (NVM) shows performance closer to DRAM, while providing terabytes of capacity, consuming less power and having a better price per byte ratio.