Your write-up made me think of:

https://codesandbox.io/blog/how-we-clone-a-running-vm-in-2-s...

Are there parallels?

I think this is very similar! Really cool to see.

The first version we launched used the exact same approach (MAP_PRIVATE). Later on, we bypassed the file system by using shared memory and using userfaultfd because ultimately the NVMe became the bottleneck (https://codesandbox.io/blog/cloning-microvms-using-userfault... and https://codesandbox.io/blog/how-we-scale-our-microvm-infrast...).