ReFlux: Reversible Compute Placement for CXL-Enabled Storage

Abstract

Static offload to computational storage devices proves brittle because device-side processors throttle under sustained thermal load, while opaque, vendor-specific interfaces inflate adoption costs so severely that no computational storage platform has achieved broad deployment; to address this, we argue that storage-side compute should be reversible, allowing individual pipeline stages to migrate between host and device at runtime beneath standard interfaces that require zero application modification. We present ReFlux, which realizes this principle on CXL SSDs by decomposing I/O-path logic into migratable storage actors compiled to WebAssembly, with actors sharing state through coherent CXL.mem regions so that only lightweight control state, roughly 8 KB, moves during migration, while a thermal-aware scheduler triggers per-stage drain-and-switch when device temperature or queue pressure rises, offloading compute-intensive actors to the host while leaving I/O-bound stages on the device. In our evaluation on an FPGA-based CXL SSD prototype and two production CSDs, ReFlux sustains over twice the throughput of thermally throttled CSDs under 30-minute sustained writes, delivers three to four times the inference throughput under KV-cache pressure, and reduces host CPU utilization by 65% through MWAIT-based notification.