131 lines
3.9 KiB
Nix
131 lines
3.9 KiB
Nix
{ config, lib, pkgs, ... }:
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let
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cfg = config.zramSwap;
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devices = map (nr: "zram${toString nr}") (lib.range 0 (cfg.swapDevices - 1));
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in
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{
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imports = [
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(lib.mkRemovedOptionModule [ "zramSwap" "numDevices" ] "Using ZRAM devices as general purpose ephemeral block devices is no longer supported")
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];
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###### interface
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options = {
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zramSwap = {
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enable = lib.mkOption {
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default = false;
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type = lib.types.bool;
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description = ''
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Enable in-memory compressed devices and swap space provided by the zram
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kernel module.
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See [
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https://www.kernel.org/doc/Documentation/blockdev/zram.txt
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](https://www.kernel.org/doc/Documentation/blockdev/zram.txt).
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'';
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};
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swapDevices = lib.mkOption {
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default = 1;
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type = lib.types.int;
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description = ''
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Number of zram devices to be used as swap, recommended is 1.
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'';
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};
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memoryPercent = lib.mkOption {
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default = 50;
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type = lib.types.int;
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description = ''
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Maximum total amount of memory that can be stored in 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. Run `zramctl` to check how good memory is compressed.
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This doesn't define how much memory will be used by the zram swap devices.
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'';
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};
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memoryMax = lib.mkOption {
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default = null;
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type = with lib.types; nullOr int;
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description = ''
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Maximum total amount of memory (in bytes) that can be stored in the zram
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swap devices.
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This doesn't define how much memory will be used by the zram swap devices.
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'';
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};
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priority = lib.mkOption {
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default = 5;
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type = lib.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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algorithm = lib.mkOption {
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default = "zstd";
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example = "lz4";
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type = with lib.types; either (enum [ "842" "lzo" "lzo-rle" "lz4" "lz4hc" "zstd" ]) str;
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description = ''
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Compression algorithm. `lzo` has good compression,
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but is slow. `lz4` has bad compression, but is fast.
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`zstd` is both good compression and fast, but requires newer kernel.
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You can check what other algorithms are supported by your zram device with
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{command}`cat /sys/class/block/zram*/comp_algorithm`
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'';
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};
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writebackDevice = lib.mkOption {
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default = null;
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example = "/dev/zvol/tarta-zoot/swap-writeback";
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type = lib.types.nullOr lib.types.path;
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description = ''
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Write incompressible pages to this device,
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as there's no gain from keeping them in RAM.
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'';
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};
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};
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};
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config = lib.mkIf cfg.enable {
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assertions = [
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{
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assertion = cfg.writebackDevice == null || cfg.swapDevices <= 1;
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message = "A single writeback device cannot be shared among multiple zram devices";
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}
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];
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services.zram-generator.enable = true;
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services.zram-generator.settings = lib.listToAttrs
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(builtins.map
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(dev: {
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name = dev;
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value =
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let
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size = "${toString cfg.memoryPercent} / 100 * ram";
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in
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{
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zram-size = if cfg.memoryMax != null then "min(${size}, ${toString cfg.memoryMax} / 1024 / 1024)" else size;
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compression-algorithm = cfg.algorithm;
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swap-priority = cfg.priority;
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} // lib.optionalAttrs (cfg.writebackDevice != null) {
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writeback-device = cfg.writebackDevice;
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};
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})
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devices);
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};
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}
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