Transparent DAX Mappings: Towards Automatic Kernel Bypass with CXL-Based Hybrid SSDs
Yussuf Khalil, Daniel Habicht, Pascal Ellinger, Frank Bellosa, Javier González, Adam Manzanares, Vivek S. Shah · 2025
Upcoming CXL-based hybrid SSDs offer a persistent memory interface in addition to traditional block-based communication. Previous research argued that the non-uniform access latencies (on-device DRAM cache hits vs. misses) of these devices call for new OS-based resource management strategies as existing DAX mechanisms were not built with this device model in mind. In this work, we sketch Transparent DAX Mappings, a novel approach to enable a broad range of applications to benefit from hybrid SSDs. By opportunistically handing out DAX mappings to processes through a collaboration between the kernel and the C standard library, we aim to achieve automatic kernel bypass for unmodified I/O-heavy applications. We evaluate a preliminary implementation of our design on a Samsung CMM-H prototype and demonstrate up to 96.2 % increased throughput in Valkey.