t3.viktorbarzin.me went down 2026-07-02 15:42-16:35 UTC: an agent-spawned
12.3G ugrep plateaued inside t3-serve@wizard's MemoryHigh(12G)..MemoryMax(16G)
band. With MemorySwapMax=0 its anon pages were unreclaimable, so the kernel
throttled every task in the cgroup indefinitely (memory.pressure full ~80%,
oom_kill never fired) - the t3 event loop starved, the accept queue rotted,
and the terminal was dead until the hog was SIGKILLed by hand.
The 2026-06-22 design assumed 'throttle to a crawl, then OOM locally'; a hog
that stabilises between high and max never OOMs, so the throttle band is a
livelock zone, not a safety layer. Viktor asked to close that gap: MemoryHigh
is now explicitly infinity on all three work cgroup definitions (t3-serve@
unit, user-<uid>.slice drop-in, docker.slice) so a runaway is cgroup-OOM-
killed at MemoryMax immediately - OOMPolicy=continue already keeps the t3
server alive when a child dies. MemoryMax/MemorySwapMax=0/earlyoom unchanged.
Applied live to the devvm the same day (daemon-reload + runtime set-property
on running cgroups, no session restarts). Post-mortem addendum + runbook
updated in the same commit.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
The systemd-oomd backstop added in the previous commit is INERT on this box.
oomd's memory-pressure kill only acts on cgroups doing active reclaim (pgscan
rising); with MemorySwapMax=0 + anonymous agent memory there is nothing to
reclaim, so pgscan stays 0 and oomd never fires. Proven live: a cgroup held at
96-99% memory.pressure for >70s with pgscan=0 was never killed (oomctl + balloon).
The very swap=0 that kills the IO storm also neuters oomd.
Replace it with earlyoom, which watches free RAM (MemAvailable%) and is
swap-independent: SIGTERM the biggest task at 5%, SIGKILL at 3%, swap ignored
(-s 100). It --avoids sshd/systemd/dockerd/containerd/t3-dispatch/tmux (the
admin's way in always survives) and --prefers the agent/browser hogs. Verified
via --dryrun: fires on the RAM threshold and selects a chrome process, not a
protected daemon.
The per-cgroup caps (MemoryHigh=12G/MemoryMax=16G/MemorySwapMax=0 per user,
docker.slice 8G) are unchanged and remain the PRIMARY guard — earlyoom is the
aggregate net for the rare all-users-maxed case. systemd-oomd purged; its config
+ ManagedOOM drop-ins removed. Post-mortem updated with the finding.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
The shared devvm keeps overloading and had to be hard-killed again today
(2026-06-22): a runaway in one user's ssh/tmux session (a 10G ugrep, plus
stacked max-effort agents) grew unbounded, spilled into the disk swap, and
swap-thrashed the throttled virtual disk into an IO storm until the box wedged.
Root cause: ssh/tmux work runs under user-<uid>.slice, left memory-uncontained
by the explicit 2026-06-10 "swap-only" decision, while only the t3-serve tree
was capped. So one user could starve everyone.
This bounds every user on BOTH trees (MemoryHigh=12G, MemoryMax=16G,
MemorySwapMax=0 so work OOMs locally at its ceiling instead of thrashing swap),
adds a systemd-oomd PSI backstop that sheds the single worst work cgroup under
box-wide pressure while leaving system.slice (sshd/services/your way in)
protected, gives system.slice a fair-share CPU/IO priority edge, and routes
docker containers into a capped, oomd-policed docker.slice so they can't dodge
the caps or mis-target oomd. All durable in setup-devvm.sh so a VM rebuild
reproduces them; systemd-oomd added to packages.txt.
Applied live and verified: oomctl shows the backstop armed (not dry-run) on the
work slices with system.slice protected; a capped-balloon stress test OOM-killed
locally at the ceiling with swap flat (no thrash).
Post-mortem: docs/post-mortems/2026-06-22-devvm-mem-io-overload-containment.md
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
