I didn't want to go into all the technical details, but we have another write-up that goes into details about RAM management: https://github.com/hocus-dev/hocus/blob/main/rfd/0003-worksp...

Other than making sure we release unused memory to the host, we didn't customize QEMU that much. Although we do have a cool layered storage solution - basically a faster alternative to QCOW2 that's also VMM independent. It's called overlaybd, and was created and implemented in Alibaba. That will probably be another blog post. https://github.com/containerd/overlaybd