First slice of BACKLOG #76 (hibernation + zram, split): zramSwap on by
default in modules/nixos/oom.nix — the memory-pressure layer before
earlyoom. zstd @ 50% RAM (nixpkgs defaults, explicit for reproducibility),
priority 100 so day-to-day paging fills zram first and any disk swapfile
stays reserved for #76's hibernate image (hibernation can't resume from
volatile zram). Follows the earlyoom mkDefault precedent — no toggle.
Adds checks.zram-swap runNixOSTest importing oom.nix, asserting the device
is an active swap, uses [zstd], and carries priority 100.
Verified: V2 checks.zram-swap PASS (/dev/zram0 in /proc/swaps, zstd,
prio 100); V1 full distro toplevel builds; V0 flake check --no-build green.
#76 remainder (disk swapfile default + resume + installer) still open.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
modules/nixos/oom.nix — running out of memory now kills the offending
process (with a desktop notification via systembus-notify) instead of
freezing the desktop for minutes until the kernel OOM killer fires.
earlyoom over systemd-oomd, deliberately: oomd kills whole cgroups,
and a Hyprland session runs as ONE scope (nothing here spawns per-app
systemd scopes, unlike GNOME) — under pressure oomd would take out the
entire desktop to save it. earlyoom kills the single largest process
before the thrash point. nixpkgs default-enables oomd in an inert
state (no slices monitored); it is disabled outright so there is one
owner. Session plumbing is --avoid-listed (unanchored — NixOS wrappers
rename comm to .foo-wrapped); no --prefer tuning, largest-RSS
selection already finds the hog. All mkDefault; opt out with
services.earlyoom.enable = false (README note added).
Verified: V0 (flake check) + V2 — new checks.oom-protection
runNixOSTest, executed: a chunked allocator (686 MB peak, 1 GB VM) is
SIGTERM'd by earlyoom in 0.1 s, a bystander unit survives (the
process-level granularity the module exists for), and systemd-oomd is
asserted inactive. 25 s runtime.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
