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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>
62 lines
2.7 KiB
Nix
62 lines
2.7 KiB
Nix
# Memory-pressure protection: keep the desktop alive when RAM runs out.
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#
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# A workstation that compiles from source WILL exhaust memory eventually —
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# a big `nix build`, a runaway eval, a browser tab. The kernel's own OOM
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# killer acts only after the system has thrashed itself unresponsive
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# (often minutes of frozen desktop) and then picks by badness score,
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# which can land on the compositor.
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#
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# earlyoom over systemd-oomd — a deliberate choice: oomd kills whole
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# cgroups, and a Hyprland session runs as ONE scope (nothing spawns
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# per-app systemd scopes here, unlike GNOME), so under pressure oomd
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# would take out the entire desktop to save it. earlyoom kills a single
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# process (highest oom_score ≈ the hog) BEFORE the thrash point — "kill
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# the build step, keep the session". nixpkgs default-enables oomd in an
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# inert state (no slices monitored); it's disabled outright below so
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# there is exactly one owner of the OOM story.
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#
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# zram sits one layer earlier: a compressed RAM swap that absorbs
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# day-to-day memory pressure (a browser's idle tabs, a big eval's cold
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# pages) before it ever reaches the earlyoom threshold — more headroom
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# on the same RAM, no disk. High swap priority so the kernel fills zram
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# first; any real disk swapfile stays reserved for the hibernate image
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# (BACKLOG #76's other half — hibernation can't resume from volatile
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# zram, so day-to-day paging must not consume the disk swap). zstd @ 50%
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# RAM are the nixpkgs defaults, kept explicit for reproducibility.
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{ lib, ... }:
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{
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zramSwap = {
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enable = lib.mkDefault true;
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algorithm = lib.mkDefault "zstd";
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memoryPercent = lib.mkDefault 50;
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# Beats any disk swapfile's auto-assigned (negative) priority, so
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# day-to-day paging lands in zram and the disk swap is left for
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# hibernation. See the header note and BACKLOG #76.
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priority = lib.mkDefault 100;
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};
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services.earlyoom = {
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enable = lib.mkDefault true;
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# Desktop toast when something is killed (relayed via
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# systembus-notify), so a vanished build/tab is explained rather
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# than mysterious.
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enableNotifications = lib.mkDefault true;
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# Never pick the session plumbing: losing the compositor or the lock
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# screen IS the outage this module exists to prevent (and killing a
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# Wayland session-lock client trips its go-to-a-tty failsafe). No
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# --prefer tuning: highest-memory selection already targets the hog.
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# Matched unanchored — NixOS wrappers rename comm to ".foo-wrapped".
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extraArgs = lib.mkDefault [
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"--avoid"
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"(Hyprland|hyprlock|greetd|waybar|pipewire|wireplumber|Xwayland|nix-daemon|systemd)"
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];
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};
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# One owner (see header): oomd ships default-on but inert; make the
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# earlyoom choice explicit and total.
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systemd.oomd.enable = lib.mkDefault false;
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}
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