pyrox.dev
nixos: Add zram swap module
This allows you to use the Linux kernel's built-in compressed memory as
swap space functionality.
It is recommended to enable only for kernel 3.14 (which is when zram came out of
the staging drivers area) or higher.
+138
nixos/modules/config/zram.nix
+138
nixos/modules/config/zram.nix
···
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{ config, lib, pkgs, ... }:
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with lib;
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let
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cfg = config.zramSwap;
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devices = map (nr: "zram${toString nr}") (range 0 (cfg.numDevices - 1));
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modprobe = "${config.system.sbin.modprobe}/sbin/modprobe";
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in
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{
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###### interface
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options = {
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zramSwap = {
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enable = mkOption {
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default = false;
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type = types.bool;
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description = ''
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Enable in-memory compressed swap space provided by the zram kernel
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module. It is recommended to enable only for kernel 3.14 or higher.
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'';
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};
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numDevices = mkOption {
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default = 4;
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type = types.int;
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description = ''
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Number of zram swap devices to create. It should be equal to the
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number of CPU cores your system has.
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'';
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};
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memoryPercent = mkOption {
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default = 50;
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type = types.int;
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description = ''
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Maximum amount of memory that can be used by the zram swap devices
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(as a percentage of your total memory). Defaults to 1/2 of your total
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RAM.
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'';
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};
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priority = mkOption {
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default = 5;
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type = types.int;
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description = ''
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Priority of the zram swap devices. It should be a number higher than
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the priority of your disk-based swap devices (so that the system will
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fill the zram swap devices before falling back to disk swap).
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'';
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};
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};
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};
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config = mkIf cfg.enable {
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system.requiredKernelConfig = with config.lib.kernelConfig; [
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(isModule "ZRAM")
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];
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# Disabling this for the moment, as it would create and mkswap devices twice,
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# once in stage 2 boot, and again when the zram-reloader service starts.
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# boot.kernelModules = [ "zram" ];
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boot.extraModprobeConfig = ''
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options zram num_devices=${toString cfg.numDevices}
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'';
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services.udev.extraRules = ''
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KERNEL=="zram[0-9]*", ENV{SYSTEMD_WANTS}="zram-init-%k.service", TAG+="systemd"
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'';
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systemd.services =
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let
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createZramInitService = dev:
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nameValuePair "zram-init-${dev}" {
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description = "Init swap on zram-based device ${dev}";
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bindsTo = [ "dev-${dev}.swap" ];
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after = [ "dev-${dev}.device" "zram-reloader.service" ];
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requires = [ "dev-${dev}.device" "zram-reloader.service" ];
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before = [ "dev-${dev}.swap" ];
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requiredBy = [ "dev-${dev}.swap" ];
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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ExecStop = "${pkgs.stdenv.shell} -c 'echo 1 > /sys/class/block/${dev}/reset'";
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};
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script = ''
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set -u
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set -o pipefail
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PATH=${pkgs.procps}/bin:${pkgs.gnugrep}/bin:${pkgs.gnused}/bin
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# Calculate memory to use for zram
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totalmem=$(free | grep -e "^Mem:" | sed -e 's/^Mem: *//' -e 's/ *.*//')
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mem=$(((totalmem * ${toString cfg.memoryPercent} / 100 / ${toString cfg.numDevices}) * 1024))
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echo $mem > /sys/class/block/${dev}/disksize
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${pkgs.utillinux}/sbin/mkswap /dev/${dev}
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'';
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restartIfChanged = false;
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};
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in listToAttrs ((map createZramInitService devices) ++ [(nameValuePair "zram-reloader"
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{
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description = "Reload zram kernel module when number of devices changes";
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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ExecStartPre = "${modprobe} -r zram";
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ExecStart = "${modprobe} zram";
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ExecStop = "${modprobe} -r zram";
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};
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restartTriggers = [ cfg.numDevices ];
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restartIfChanged = true;
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})]);
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swapDevices =
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let
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useZramSwap = dev:
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{
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device = "/dev/${dev}";
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priority = cfg.priority;
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};
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in map useZramSwap devices;
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};
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}