diff options
author | danbst <abcz2.uprola@gmail.com> | 2018-12-28 00:00:48 +0200 |
---|---|---|
committer | danbst <abcz2.uprola@gmail.com> | 2019-01-17 15:58:53 +0200 |
commit | 8d8a7210e480ac122d55a7d36879b8f41ea6fc80 (patch) | |
tree | e703f5cf360f84cd6ad819c7ecd7237173c101fb /nixos/modules/config/zram.nix | |
parent | 872502aa56bd4d574fcfe9cfef9066c9e8ee2894 (diff) |
zramSwap: allow configure compression algorithm + cleanups
- add `zramSwap.algorithm` option, which allows to change compressor
declaratively. zstd as default
- add `zramSwap.swapDevices` option, which allows to define how many zram
devices will be used as swap. Rest devices can be managed freely
- simpler floating calculations
- fix udev race condition
- some documentation changes
- replaced `/sys/block/zram*` handling with `zramctl`, because I had occasional
"Device is busy" error (looks like zram has to be configured in predefined order)
- added `memoryPercent` and `algorithm` as restart triggers. I think, it was
a bug that changing `memoryPercent` in configuration wasn't applied immediately.
- removed a bind to .swap device. While it looks natural (when swap device goes
off, so should zram device), it wasn't implemented properly. This caused problems
with swapon/swapoff:
```
$ cat /proc/swaps
Filename Type Size Used Priority
/dev/zram0 partition 8166024 0 -2
/var/swapfile file 5119996 5120 1
$ sudo swapoff -a
$ sudo swapon -a
swapon: /dev/zram0: read swap header failed
$ cat /proc/swaps
Filename Type Size Used Priority
/var/swapfile file 5119996 0 1
```
Diffstat (limited to 'nixos/modules/config/zram.nix')
-rw-r--r-- | nixos/modules/config/zram.nix | 79 |
1 files changed, 65 insertions, 14 deletions
diff --git a/nixos/modules/config/zram.nix b/nixos/modules/config/zram.nix index c1748812821e..f8ff926cd56d 100644 --- a/nixos/modules/config/zram.nix +++ b/nixos/modules/config/zram.nix @@ -6,10 +6,27 @@ let cfg = config.zramSwap; - devices = map (nr: "zram${toString nr}") (range 0 (cfg.numDevices - 1)); + # don't set swapDevices as mkDefault, so we can detect user had read our warning + # (see below) and made an action (or not) + devicesCount = if cfg.swapDevices != null then cfg.swapDevices else cfg.numDevices; + + devices = map (nr: "zram${toString nr}") (range 0 (devicesCount - 1)); modprobe = "${pkgs.kmod}/bin/modprobe"; + warnings = + assert cfg.swapDevices != null -> cfg.numDevices >= cfg.swapDevices; + flatten [ + (optional (cfg.numDevices > 1 && cfg.swapDevices == null) '' + Using several small zram devices as swap is no better than using one large. + Set either zramSwap.numDevices = 1 or explicitly set zramSwap.swapDevices. + + Previously multiple zram devices were used to enable multithreaded + compression. Linux supports multithreaded compression for 1 device + since 3.15. See https://lkml.org/lkml/2014/2/28/404 for details. + '') + ]; + in { @@ -24,9 +41,11 @@ in default = false; type = types.bool; description = '' - Enable in-memory compressed swap space provided by the zram kernel - module. - See https://www.kernel.org/doc/Documentation/blockdev/zram.txt + Enable in-memory compressed devices and swap space provided by the zram + kernel module. + See <link xlink:href="https://www.kernel.org/doc/Documentation/blockdev/zram.txt"> + https://www.kernel.org/doc/Documentation/blockdev/zram.txt + </link>. ''; }; @@ -34,7 +53,19 @@ in default = 1; type = types.int; description = '' - Number of zram swap devices to create. + Number of zram devices to create. See also + <literal>zramSwap.swapDevices</literal> + ''; + }; + + swapDevices = mkOption { + default = null; + example = 1; + type = with types; nullOr int; + description = '' + Number of zram devices to be used as swap. Must be + <literal><= zramSwap.numDevices</literal>. + Default is same as <literal>zramSwap.numDevices</literal>, recommended is 1. ''; }; @@ -44,7 +75,8 @@ in 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. + RAM. Run <literal>zramctl</literal> to check how good memory is + compressed. ''; }; @@ -58,12 +90,26 @@ in ''; }; + algorithm = mkOption { + default = "zstd"; + example = "lzo"; + type = with types; either (enum [ "lzo" "lz4" "zstd" ]) str; + description = '' + Compression algorithm. <literal>lzo</literal> has good compression, + but is slow. <literal>lz4</literal> has bad compression, but is fast. + <literal>zstd</literal> is both good compression and fast. + You can check what other algorithms are supported by your zram device with + <programlisting>cat /sys/class/block/zram*/comp_algorithm</programlisting> + ''; + }; }; }; config = mkIf cfg.enable { + inherit warnings; + system.requiredKernelConfig = with config.lib.kernelConfig; [ (isModule "ZRAM") ]; @@ -85,7 +131,6 @@ in 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-${dev}.swap" ]; @@ -96,14 +141,14 @@ in ExecStop = "${pkgs.runtimeShell} -c 'echo 1 > /sys/class/block/${dev}/reset'"; }; script = '' - set -u - set -o pipefail - + set -euo pipefail + # Calculate memory to use for zram - totalmem=$(${pkgs.gnugrep}/bin/grep 'MemTotal: ' /proc/meminfo | ${pkgs.gawk}/bin/awk '{print $2}') - mem=$(((totalmem * ${toString cfg.memoryPercent} / 100 / ${toString cfg.numDevices}) * 1024)) + mem=$(${pkgs.gawk}/bin/awk '/MemTotal: / { + print int($2*${toString cfg.memoryPercent}/100.0/${toString devicesCount}*1024) + }' /proc/meminfo) - echo $mem > /sys/class/block/${dev}/disksize + ${pkgs.utillinux}/sbin/zramctl --size $mem --algorithm ${cfg.algorithm} /dev/${dev} ${pkgs.utillinux}/sbin/mkswap /dev/${dev} ''; restartIfChanged = false; @@ -111,6 +156,8 @@ in in listToAttrs ((map createZramInitService devices) ++ [(nameValuePair "zram-reloader" { description = "Reload zram kernel module when number of devices changes"; + wants = [ "systemd-udevd.service" ]; + after = [ "systemd-udevd.service" ]; serviceConfig = { Type = "oneshot"; RemainAfterExit = true; @@ -118,7 +165,11 @@ in ExecStart = "${modprobe} zram"; ExecStop = "${modprobe} -r zram"; }; - restartTriggers = [ cfg.numDevices ]; + restartTriggers = [ + cfg.numDevices + cfg.algorithm + cfg.memoryPercent + ]; restartIfChanged = true; })]); |