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Comment by nu11ptr | Hacker News Reader

> For faster startup, lower memory footprint and so on

Any idea how they do this? My WSL2 starts insanely fast, like about 1-2 seconds. I've never seen a linux distro natively boot that fast. Assuming they suppress any sort of BIOS startup screen for starters, but what else?

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It’s a very trimmed down kernel with minimal set of drivers and modules. It doesn’t even support SD cards out of the box. That’s probably the main reason as no hardware probing/initialization delays are incurred.

At high level, WSL2 provides a single optimized VM and Microsoft-compiled Linux kernel. Optimized here means that the VM only provides a small set of devices to the Linux kernel, and the kernel operates with exact known hardware, which is much smaller and simpler compared to a full blown kernel (which detects a large variety of hardware) and fuller featured VMs (c.f. qemu emulated devices: https://kashyapc.fedorapeople.org/virt/qemu/qemu-list-of-emu...).

And when you run multiple "distributions" or instances, they all share the same running VM and kernel. So after a one-time startup of the VM+kernel, opening more distributions/instances is like starting new system containers (similar to lxc/lxd or systemd-nspawn, which are also very quick to spawn on Linux) rather than new VMs. The architecture is quite similar to Linux-on-ChromeOS (Crostini).

Actually I don't know it either. But WSL2 doesn't really start a lot of processes, like a desktop/server Linux distribution. It starts up only a minimal set of processes, and a shell.

dmesg looks like the kernel is booting up normally, so I guess they don't use some memory snapshots magic.

I guess they just tweaked the kernel and the hypervisor to start up fast. There is also no BIOS/UEFI delay.

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