CXLResume: Retained-State Checkpoint and Restore for In-Memory Services
Checkpointing and restoring an in-memory service typically require writing its memory pages to checkpoint images and refilling them at the destination. When application state already resides in shared memory that remains accessible after failover, copying those pages into and out of checkpoint images is unnecessary. We present CXLResume, a prototype that retains the service's main heap objects in shared memory while checkpointing the remaining execution state and mapping metadata. Checkpointing preserves the shared heap at the same freeze point as the serialized process state. During recovery, CXLResume remaps the same shared memory at its original virtual addresses before restoring execution, preserving direct pointers within and across shared and private memory. We evaluate CXLResume with Redis and Memcached using QEMU CXL functional emulation. At 6 GiB, CXLResume reduces combined checkpoint and restore time from 15.015 s to 0.242 s for Redis and from 19.770 s to 0.276 s for Memcached in the evaluated deployments. These results show that retaining shared application state removes large application heaps from the checkpoint data path and substantially reduces checkpoint and restore latency.