Uses for CXL memory

Posted Apr 17, 2025 15:27 UTC (Thu) by farnz (subscriber, #17727)
In reply to: Uses for CXL memory by gmprice
Parent article: Management of volatile CXL devices

I can't comment in detail, because of NDAs, but yes, they do, because they already have the bin packing problem, and CXL moves when you deal with it from "building the DC" to "while operating the DC".

Today, you typically build a rack of either compute-optimized, general purpose or memory-optimized servers, and you get most active servers per rack if they're compute-optimized (since you can't actually power up all 42U or whatever height you have of rack at once, due to cooling and power constraints), and fewest if they're memory-optimized. This forces you into a balancing act; you want to bias towards compute-optimized servers, but you need enough general purpose and memory-optimized servers to handle workloads that need more RAM than a compute-optimized server has.

The CXL memory promise is that you have only compute-optimized racks with powered-down CXL memory devices in the rack. If you need general purpose or memory-optimized servers, you power down some compute-optimized servers to power up some CXL memory, and change the rack configuration from (numbers invented) 10 compute-optimized servers to 3 memory-optimized servers and 3 compute-optimized on the fly. When the workload balance changes (and you pressure your internal teams to get the balance to change if at all possible, because of the aforementioned power and cooling limits), you switch the rack back to compute-optimized servers.