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 ```
This commit is contained in:
danbst
parent
872502aa56
commit
8d8a7210e4
@ -408,6 +408,21 @@
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from nixpkgs due to the lack of maintainers.
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</para>
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</listitem>
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<listitem>
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<para>
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It is possible now to uze ZRAM devices as general purpose ephemeral block devices,
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not only as swap. Using more than 1 device as ZRAM swap is no longer recommended,
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but is still possible by setting <literal>zramSwap.swapDevices</literal> explicitly.
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</para>
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<para>
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Default algorithm for ZRAM swap was changed to <literal>zstd</literal>.
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</para>
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<para>
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Changes to ZRAM algorithm are applied during <literal>nixos-rebuild switch</literal>,
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so make sure you have enough swap space on disk to survive ZRAM device rebuild. Alternatively,
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use <literal>nixos-rebuild boot; reboot</literal>.
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</para>
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</listitem>
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</itemizedlist>
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</section>
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</section>
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@ -6,10 +6,27 @@ let
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cfg = config.zramSwap;
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devices = map (nr: "zram${toString nr}") (range 0 (cfg.numDevices - 1));
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# don't set swapDevices as mkDefault, so we can detect user had read our warning
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# (see below) and made an action (or not)
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devicesCount = if cfg.swapDevices != null then cfg.swapDevices else cfg.numDevices;
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devices = map (nr: "zram${toString nr}") (range 0 (devicesCount - 1));
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modprobe = "${pkgs.kmod}/bin/modprobe";
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warnings =
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assert cfg.swapDevices != null -> cfg.numDevices >= cfg.swapDevices;
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flatten [
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(optional (cfg.numDevices > 1 && cfg.swapDevices == null) ''
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Using several small zram devices as swap is no better than using one large.
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Set either zramSwap.numDevices = 1 or explicitly set zramSwap.swapDevices.
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Previously multiple zram devices were used to enable multithreaded
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compression. Linux supports multithreaded compression for 1 device
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since 3.15. See https://lkml.org/lkml/2014/2/28/404 for details.
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'')
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];
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in
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{
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@ -24,9 +41,11 @@ in
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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.
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See https://www.kernel.org/doc/Documentation/blockdev/zram.txt
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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 <link xlink:href="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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</link>.
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'';
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};
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@ -34,7 +53,19 @@ in
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default = 1;
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type = types.int;
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description = ''
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Number of zram swap devices to create.
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Number of zram devices to create. See also
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<literal>zramSwap.swapDevices</literal>
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'';
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};
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swapDevices = mkOption {
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default = null;
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example = 1;
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type = with types; nullOr int;
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description = ''
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Number of zram devices to be used as swap. Must be
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<literal><= zramSwap.numDevices</literal>.
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Default is same as <literal>zramSwap.numDevices</literal>, recommended is 1.
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'';
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};
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@ -44,7 +75,8 @@ in
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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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RAM. Run <literal>zramctl</literal> to check how good memory is
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compressed.
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'';
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};
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@ -58,12 +90,26 @@ in
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'';
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};
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algorithm = mkOption {
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default = "zstd";
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example = "lzo";
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type = with types; either (enum [ "lzo" "lz4" "zstd" ]) str;
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description = ''
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Compression algorithm. <literal>lzo</literal> has good compression,
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but is slow. <literal>lz4</literal> has bad compression, but is fast.
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<literal>zstd</literal> is both good compression and fast.
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You can check what other algorithms are supported by your zram device with
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<programlisting>cat /sys/class/block/zram*/comp_algorithm</programlisting>
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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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inherit warnings;
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system.requiredKernelConfig = with config.lib.kernelConfig; [
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(isModule "ZRAM")
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];
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@ -85,7 +131,6 @@ in
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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-${dev}.swap" ];
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@ -96,14 +141,14 @@ in
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ExecStop = "${pkgs.runtimeShell} -c 'echo 1 > /sys/class/block/${dev}/reset'";
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};
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script = ''
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set -u
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set -o pipefail
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# Calculate memory to use for zram
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totalmem=$(${pkgs.gnugrep}/bin/grep 'MemTotal: ' /proc/meminfo | ${pkgs.gawk}/bin/awk '{print $2}')
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mem=$(((totalmem * ${toString cfg.memoryPercent} / 100 / ${toString cfg.numDevices}) * 1024))
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set -euo pipefail
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echo $mem > /sys/class/block/${dev}/disksize
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# Calculate memory to use for zram
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mem=$(${pkgs.gawk}/bin/awk '/MemTotal: / {
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print int($2*${toString cfg.memoryPercent}/100.0/${toString devicesCount}*1024)
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}' /proc/meminfo)
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${pkgs.utillinux}/sbin/zramctl --size $mem --algorithm ${cfg.algorithm} /dev/${dev}
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${pkgs.utillinux}/sbin/mkswap /dev/${dev}
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'';
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restartIfChanged = false;
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@ -111,6 +156,8 @@ in
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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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wants = [ "systemd-udevd.service" ];
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after = [ "systemd-udevd.service" ];
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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@ -118,7 +165,11 @@ in
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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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restartTriggers = [
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cfg.numDevices
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cfg.algorithm
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cfg.memoryPercent
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];
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restartIfChanged = true;
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})]);
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