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by dataflow 383 days ago
VirtualBox on Windows, primarily. Though I feel like haven't seen other VMs in the past start up a whole ton faster (maybe a somewhat) (ignoring WSL2). Page files are already disabled, there's plenty of free RAM, and it makes no difference how little RAM the guest is allocated (even if it's 256MB). So no, those are not the issues. VirtualBox itself seems to be doing something slow during that time and I don't know what that is.
3 comments
gopher_space 383 days ago
I remembered something about VirtualBox not playing nicely with Hyper-V on Windows, and dug up a possibly relevant post[0] on their forums. IIRC we ended up moving a few build systems to Docker and dropping VirtualBox because of hyper-v related issues, but it's been a few years.

[0] https://forums.virtualbox.org/viewtopic.php?t=112113

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dataflow 383 days ago
That's the unrelated green-turtle issue. It's only relevant after the guest has actually started running instructions. I'm talking about before that point.
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gopher_space 383 days ago
I'm not aware of any turtles, that was just the first thing I found when trying to see if VirtualBox and Hyper-V were still a problematic combo.

Again, it was a few years ago, but we didn't solve the problem or identify an actual root cause. We stopped banging our heads against that particular wall and switched technologies.

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mgerdts 382 days ago
What is your definition of free memory? If the system has read a lot of data, the page cache is probably occupying most of the RAM you consider free. Look at cache and standby counters.

I’ve noticed that windows can only evict data from the page cache at about 5 GB/s. I do not know if this zeros the memory or that would need to be done in the allocation path.

A couple years ago I tracked down a long pause while starting qemu on Linux to it zeroing the 100s of GB of RAM given to the VM as 1 GB huge pages.

These may or may not be big contributors to what you are seeing, depending on the VM’s RAM size.

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mynameisvlad 383 days ago
So the issue is pretty clearly with VirtualBox itself, but you are making it sound like it's an issue with VMs on Windows or in general.
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