Tidying Up the Address Space

Abstract: Memory tiering in datacenters does not achieve its full potential due to hotness fragmentation -- the intermingling of hot and cold objects within memory pages. This fragmentation prevents page-based reclamation systems from distinguishing truly hot pages from pages containing mostly cold objects, fundamentally limiting memory efficiency despite highly skewed accesses. We introduce address-space engineering: dynamically reorganizing application virtual address spaces to create uniformly hot and cold regions that any page-level tiering backend can manage effectively. HADES demonstrates this frontend/backend approach through a compiler-runtime system that tracks and migrates objects based on access patterns, requiring minimal developer intervention. Evaluations across ten data structures achieve up to 70% memory reduction with 3% performance overhead, showing that address space engineering enables existing reclamation systems to reclaim memory aggressively without performance degradation.