The article did an ok job of explaining the firecracker limitations they ran into but it was extremely skimpy when it came to qemu and just rushed to the conclusion “we did a lot of work so try our product.”
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
