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

Original Article ↗ Hacker News Discussion ↗

How small and fast a macOS virtual machine can be becomes a springboard for examining Apple’s memory management, virtualization features, and the trade-offs of running macOS in constrained environments. Commenters weigh how little RAM and CPU a usable macOS VM can get by with, how well it handles memory pressure compared to Linux and Windows, and where bugs like memory leaks undermine that efficiency. They also explore tooling such as Apple’s virtualization framework, container CLI, and third-party options for containers and GPU-accelerated workloads, highlighting both impressive performance on Apple Silicon and practical gaps for development and CI use.

Apple Silicon vs Intel & macOS VM Performance

  • Multiple comments report Apple Silicon Airs “stomping” comparable Intel MacBooks on general workloads, with big wins in performance and thermals (silent vs “hairdryer” fans).
  • A Geekbench comparison is cited showing ~2.5× CPU score improvement for a newer MacBook over a 2020 Intel Air.
  • Some users still find specific tools (e.g., iOS Safari via Xcode simulator on Intel) sluggish and are hopeful Apple Silicon will resolve this.

Memory Usage, Ballooning & Stability

  • Discussion around a macOS VM using less RAM than allocated: some assumed no ballooning; others link to Apple’s virtualization docs showing a balloon device exists (though not for macOS guests).
  • Several argue macOS manages memory well under desktop multitasking; others counter with examples of system apps leaking memory and causing OOM, especially in recent macOS versions.
  • There’s disagreement whether these represent widespread systemic issues or isolated bugs.

Core Count, RAM & Build/Compute Workloads

  • Observations that macOS VM memory usage shrinks as both RAM and vCPUs are reduced; most attribute this to the OS adapting cache/buffer usage, not per-CPU overhead.
  • Multiple comments stress that physical RAM should scale with hardware threads, especially for parallel builds (Chrome, Vivado, FlashAttention) that can require gigabytes per thread and force lowering -j when RAM is constrained.

Containers & VM Tooling on macOS

  • Experiences with colima/docker range from “usable but painful/inefficient” to acceptable; limactl and podman are also mentioned.
  • Apple’s container CLI receives praise for speed and integration, but lacks Docker CLI compatibility and Compose support, which some find limiting or “typical Apple.”
  • OrbStack is widely praised for performance and energy efficiency via a single-VM-plus-containers model, but its closed-source, per-seat licensing is a blocker for some.

Security, Signing & Notarization Automation

  • One user’s 200-line Bash script for unattended signing/notarization is criticized as overcomplicated; others note keychain unlocking and avoiding GUI prompts add real complexity in CI contexts.
  • There’s disagreement on how minimal such automation can be, but consensus that non-interactive setups are fragile.

GPU & ML in VMs/Containers

  • A new M5 Air user struggles to get PyTorch with GPU acceleration inside isolated environments; virtio-gpu exposes graphics but not compute.
  • Some mention emerging approaches (e.g., Docker Model Runner, podman+libkrun) but characterize Vulkan-based workarounds as experimental and slow.
  • At least one person reports getting PyTorch’s MPS backend working inside a macOS VM using a Tart image, though only minimal tests were run.

Minimal macOS / Darwin / XNU

  • Curiosity about stripping macOS to a bare, possibly non-GUI system leads to discussion of Darwin/XNU layers and the long-running PureDarwin project (currently in need of new leadership).
  • Apple’s XNU source has moved to a different GitHub org and is still updated, but rebuilding/booting it is seen as a “fun but costly” side project.
  • Instructions are shared for booting modern Macs directly into a root shell (single-user mode) via reduced security settings and nvram flags.

Networking, Tailscale & Identity in Containers

  • An example project shows using Apple’s container tooling plus Tailscale SSH so each container gets its own Tailnet IP/identity, separate from the host.
  • This is positioned as useful for letting others in the Tailnet access a containerized app without exposing the whole Mac or resorting to port forwarding.

macOS on PCs & Remote Dev

  • Running macOS on PC is described as possible via QEMU or “Hackintosh,” but with missing features (e.g., hardware-accelerated graphics, Secure Enclave–dependent services like Apple Pay, iMessage, FaceTime).
  • One brief question about enrolling a macOS VM into Intune gets the answer that it’s likely only straightforward as BYOD; company-owned enrollment ties into Apple Business Manager.