The comparison between RMA based memory disaggregation and CXL.mem based memory disaggregation.
The span+coherency state in Carbink is just like cacheline coherency in CXL.mem but except that if two threads contention on one span it will go back and forth, that's the charm of cachable that CXL don't need the cacheline be transmitted but they are registered in the window of local LLC.
A lot of the software optimization is based on the panelty of small chunks transmission of RDMA is too huge that if we replace with CXL, we don't need to care ptr serialization and relinking because they are in the same memory space. maintaining a metadata of pages is still a huge overhead. The local page map is a two-level radix tree. The lookup process is similar to a page table walk: the first 20 bits of the object's virtual address are indexed to the first level radix tree table, and the next 15 bits are indexed to the second level table. The same mapping method allows Carbink to map the virtual address of a locally-resident span to its metadata. Thus this paper in era of CXL is useless, nothing to refer.
The difference of EC-Split(their implementation of Hydra) and EC-Batch is the critical path of the memory transaction. To reconstruct a single span, a compute node must contact multiple memory nodes to pull in all the required fragments. This requirement to contact multiple memory nodes makes the swap operation vulnerable to deviators, thus increasing the tail latency. And their compaction and de-fragmentation approach is to save the remote data usage but has no upgain for performance actually for their local vs remote upper than 50%. They only gain 10% for more on local side by the hiding of the span swap operations.
