nixpkgs/nixos/modules/config/zram.nix
Ricardo M. Correia cd1b48bc35 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.
2014-05-06 20:04:22 +02:00

139 lines
3.9 KiB
Nix

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