How fast is a macOS VM, and how small could it be?

mmoosia about 4 hours ago 28 commentsRead Article on eclecticlight.co

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fouc•about 3 hours ago

>Starting with 4 virtual cores and 8 GB vRAM, where the VM ran perfectly briskly with around 5 GB of memory used, I stepped down to 3 cores and 6 GB, to discover that memory usage fell to 3.9 GB and everything worked well. With just 2 cores and 4 GB of memory only 3.1 GB of that was used, and the VM continued to handle those lightweight tasks normally.

Good reminder that there's a certain amount of memory tied up with each core (probably mainly page cache and concurrency handling etc).

fulafel•18 minutes ago

I'd bet for the null hypothesis: the memory behaviour changes would hold if the core count was kept constant and only the VM's memory size was adjusted.

brookst•14 minutes ago

Agreed. This is the OS adapting to available memory.

Similarly if you started with 4GB and there was 900MB available for user apps, I expect you could launch apps that consume 1500MB just fine; the OS is leaving enough to launch anything, and making use of unused memory for cache/etc.

wutwutwat•8 minutes ago

There is some overhead per-core, you're right, but imo this reduction in usage is likely from how the kernel allocates available memory, which is being reduced as well. The kernel will keep read caches around longer with more memory, it'll prefer to compress memory instead of swap to disk if it has more, it'll purge/cleanup reclaimable memory less often with more memory, etc. It even scales its internal buffer sizes and vnode tables depending on total memory.

All good things imo, it dynamically makes the most of what is available, at the expense of making it harder to see a true baseline of hard min requirement to operate.

Fun things to check, `vm_stat`

$ vm_stat Mach Virtual Memory Statistics: (page size of 4096 bytes)

Pages free: 230295.

Pages active: 1206857.

Pages inactive: 1206361.

Pages speculative: 31863.

Pages throttled: 0.

Pages wired down: 470093.

Pages purgeable: 18894.

"Translation faults": 21635255.

Pages copy-on-write: 1590349.

Pages zero filled: 11093310.

Pages reactivated: 15580.

Pages purged: 50928.

File-backed pages: 689378.

Anonymous pages: 1755703.

Pages stored in compressor: 0.

Pages occupied by compressor: 0.

Decompressions: 0.

Compressions: 0.

Pageins: 832529.

Pageouts: 225.

Swapins: 0.

Swapouts: 0.

edit: no code fence markdown support or am I doing something wrong?

Havoc•about 2 hours ago

Got a M5 air recently - my first dive into MacOS land so trying to figure this out too.

Seems essentially impossible to get:

* pytorch

* GPU acceleration

* VM/container like isolation

The virtio-gpu layer gets closest but seems to only pass through graphics GPU not compute GPU so no pytorch

emmelaich•19 minutes ago

I got torch to run in a Cirruslabs Tart instance.

plufz•about 1 hour ago

I need this too, and looked quite a lot on it a year ago. I haven’t had time to check out the recent developments with Docker Model Runner (vllm-metal) or podman libkrun. Did neither of those work for you?

Havoc•20 minutes ago

vllm-metal isn't GPU access but rather a openai compatible end point which I can already do via lm studio endpoint over network

>podman libkrun

Haven't tried it but research suggests its really shaky still. podman libkrun exposes vulkan while torch expects mps on macs. Sounds like one can force vulkan but that's apparently slow and beta-ish?

nasretdinov•about 2 hours ago

Honestly macOS probably can go much lower than that if you turn off some stuff that's not strictly necessary for a VM. The first iPhones only had 128 MiB of RAM and they ran a trimmed down version of macOS Tiger I believe. It's just that RAM has been quite abundant so far, so there was no real reason to try to trim it down, but it's definitely possible, and probably not that hard either, we just need to start trying again :)

dhruv3006•about 1 hour ago

https://github.com/trycua/cua/tree/main/libs/lume had a interesting take on this.

nottorp•about 3 hours ago

> Starting with 4 virtual cores and 8 GB vRAM, where the VM ran perfectly briskly with around 5 GB of memory used

But... if you start applications inside your VM it will want the full 8 Gb you've allocated not the 5 Gb it uses at startup?

stingraycharles•about 3 hours ago

I don’t assume that macOS virtualization is advanced enough to support memory ballooning, or is that not what you’re referring to?

Edit: I stand corrected!

pyth0•about 3 hours ago

I don't assume anything either, but a single Google search is enough to dispel that [1]

[1] https://developer.apple.com/documentation/virtualization/vzv...

sgt•about 3 hours ago

macOS is generally pretty amazing at efficient memory usage and VM (virtual memory subsystem) handling. So even a 8GB machine can run pretty impressive workloads without having the user think the machine is underpowered.

p_ing•about 1 hour ago

Not really. Larger page sizes mean more potential for wasted memory and it has had a long standing memory leak in some core component to where even Calculator can cause an OOM event.

nottorp•about 3 hours ago

What will that help with if the host and guest combined need > physical ram?

jdub•about 2 hours ago

If guest memory can be reclaimed, it doesn't need to be paged to disk once you hit RAM contention. It's mostly saving accounting overhead, but it'll have some effect on latency, which you're more likely to perceive under contention.

collabs•about 1 hour ago

I was hoping to see the bare macOS with all the applications removed as much as possible, no graphical user interface, just the bare minimum to boot, login as a user, and write hello world dot txt with a text editor. Or maybe some command line apps? Or is it no longer macOS at that point?

hmry•about 1 hour ago

"I'd just like to interject for a moment. What you're referring to as macOS, is in fact, macOS/Darwin, or as I've recently taken to calling it, macOS plus Darwin."

"What you're referring to as Darwin, is in fact, Darwin/XNU."

"What you're referring to as XNU, is in fact, BSD/Mach."

I seem to remember it being possible to run macOS-less Darwin several years ago, not sure if that's still possible or if Apple has modified it so much at this point that it's useless without at least some macOS components.

Terretta•6 minutes ago

> several years ago

2024, maybe? needs some renewed interest perhaps:

https://www.puredarwin.org/

mgaunard•about 2 hours ago

My only experience with VMs on macOS is colima+docker, and it's relatively painful and inefficient (but usable).

woadwarrior01•2 minutes ago

Try Apple's container CLI. I moved a project of mine from colima+docker to it relatively easily, a couple of weekends ago.

https://github.com/apple/container

embedding-shape•about 2 hours ago

Recently got a Mac Mini for local CI purposes (together with Forgejo Actions), took a broad look at the ecosystem and decided to just roll with "build on host" instead. Setting up signing/notarization just looked like an insurmountably task together with isolating it from the host, even with agents. At least the macOS builds are really fast now and the signing/notarization just ~200 lines of Bash...

latexr•about 2 hours ago

> the signing/notarization just ~200 lines of Bash

200 lines?! That’s two orders of magnitude too many. What exactly are you doing that you need so such code for signing and notarisation?

yohannparis•about 2 hours ago

Could you share your recipe please ? I’m interested

dieulot•about 3 hours ago

I'm wondering if the Xcode simulator (without Xcode running) performs as well, my 2020 Intel MacBook Air has been incapable of running Safari in iOS smoothly for nearly all its life.