Gregory Price and his team at Meta developed CRAM, a new technology designed to improve compressed memory performance in Linux. Unlike ZRAM, which functions as swap, CRAM operates entirely within memory by utilizing a private NUMA node. This approach allows the system to maintain standard memory semantics, including migration and ballooning.
The technology incorporates a mechanism called the Chicken Bit to prevent cascading failures, known as a poison storm, during allocation processes. While CRAM currently faces challenges in determining logical RAM capacity when data compressibility varies, it aims to provide significant performance gains for Linux servers and potentially other devices like the Steam Deck.
Performance benchmarks highlight a substantial advantage over ZRAM. In read-only scenarios, CRAM achieved 489 million operations per second compared to 1.1 million for ZRAM, representing a 452x speedup. Even with a 20% write load, CRAM demonstrated a 5.4x speedup over ZRAM, though performance decreases due to the necessity of paging and migrating folios.
