Lost Bytes At The Crossroads Between User-And Kernel-Level Memory Management

Abstract

With soaring DRAM prices, optimizing software for efficient memory use is becoming increasingly important. Essential to this end is the memory management component of the software's language runtime. This component requests page-sized memory from the kernel and subdivides it into smaller blocks to satisfy allocations performed by the software. Since DRAM was comparatively cheap for the preceding decade, contemporary prior work has focused on optimizing this component for performance. A key optimization is conducted on the free path where memory freed by the software is not directly returned to the kernel to satisfy future allocations and avoid costly context switches. In this work-in-progress paper, we illustrate the lost potential of user-level allocators for system-wide memory use. We show that—since the kernel manages memory at page-granularity—the user-level allocation scheme must be designed with page alignment in mind. We provide a classification for physical memory that is lost due to the mismatch of user-space and kernel-space allocation granularities. To empirically illustrate the potential of such an allocation scheme, we conduct experiments with the mallocng allocator where we identify potential savings of up to 75 percent.