reference console kvm ram highwater mark 20260715T111910

Console's hypervisor (KVM) process on Finn holds host RAM at whatever high-water mark the guest has ever touched, and never gives it back without a balloon driver (qm set 103 --balloon <min>). So Console's allocated 80G (memory: 81920 in qm config 103) shows as ~75G resident on Finn even when the guest's own free-memory accounting says it's only using 22G internally, because a prior compile storm touched ~73G (93%) and that's now the sticky floor.

Why: This caused real confusion ("Finn is at 97G, how is that possible if I'm at 88 inside Console?") and matters for capacity planning: Finn must be sized as if Console always uses its full allocation, not its current steady-state usage.

How to apply: When reasoning about Finn's free RAM or whether to raise Console's memory ceiling, use Console's allocated size, not its current internal usage, as the worst-case number. Ballooning is available as a lever to let Proxmox reclaim idle guest pages under host pressure, but tradeoff is it can throttle Console mid-build. As of 2026-07-15 the team chose to leave ballooning off and keep Console at 80G (not raise to 95G); 88G was floated as a defensible ceiling if headroom is ever needed. See also Finn 128GB upgrade.

[auto-memory session 60d132de-4659-485c-8044-427af0ccce7f, confidence 0.65, mode staged]