[TUHS] VM over-commit (and the OOM killers)

[Arrigo Triulzi via TUHS]

On 28 Feb 2025, at 20:36, Greg A. Woods <woods at robohack.ca> wrote:
> That's probably mostly true, but also misguided and ignorant of the
> actual behaviour of RAM-starved systems.  I suspect it was policy based
> on memory prices at some time in the past, but seemingly hasn't been
> re-evaluated for modern workloads more recently.

I strongly agree: as an old Unix hand hitting swap was something you wanted to avoid at all cost, except for certain cases where swap use could be replaced by accurate use of files to swap data in and out of RAM during programme execution because of the predictability of data accesses. It was still bad programming but not as lethal as thrashing.

The current macOS is a disappointment in that respect: on a 64GB machine when running the Apple Virtualisation Framework for VMs (UTM and Parallels) I am surprised at how just a couple of 8GB VMs can send the VMM into a frenzy.

My FreeBSD bhyve hosts with similar memory and VM load do not exhibit this behaviour at all, despite ZFS ARC.

Arrigo