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Dynamic memory management - Firecracker's RAM footprint starts low, but once a workload inside allocates RAM, Firecracker will never return it to the host system. After running several workloads inside, you end up with an idling VM that consumes 32 GB of RAM on the host, even though it doesn't need any of it.
Firecracker has a balloon device you can inflate (ie: acquire as much memory inside the VM as possible) and then deflate... returning the memory to the host.
https://github.com/firecracker-microvm/firecracker/blob/main...
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
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
There is no mention of cloud-hypervisor[1] (also in the rust-vmm ecosystem) in the article. It has the memory reclamation feature they require. It also support VFIO and virtiofs.
[1] <https://github.com/cloud-hypervisor/cloud-hypervisor>
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