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Merge pull request #52991 from danbst/zram-zstd

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zramSwap: allow configure compression algorithm + cleanups
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Danylo Hlynskyi 2019-01-23 09:30:55 +02:00 committed by GitHub
commit ab31b13401
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2 changed files with 83 additions and 15 deletions
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15
nixos/doc/manual/release-notes/rl-1903.xml
View File

@ -408,6 +408,21 @@
from nixpkgs due to the lack of maintainers.
</para>
</listitem>
<listitem>
<para>
It is possible now to uze ZRAM devices as general purpose ephemeral block devices,
not only as swap. Using more than 1 device as ZRAM swap is no longer recommended,
but is still possible by setting <literal>zramSwap.swapDevices</literal> explicitly.
</para>
<para>
Default algorithm for ZRAM swap was changed to <literal>zstd</literal>.
</para>
<para>
Changes to ZRAM algorithm are applied during <literal>nixos-rebuild switch</literal>,
so make sure you have enough swap space on disk to survive ZRAM device rebuild. Alternatively,
use <literal>nixos-rebuild boot; reboot</literal>.
</para>
</listitem>
</itemizedlist>
</section>
</section>

83
nixos/modules/config/zram.nix
View File

@ -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>&lt;= 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")
];
@ -85,25 +131,25 @@ 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-${dev}.swap" ];
requiredBy = [ "dev-${dev}.swap" ];
unitConfig.DefaultDependencies = false; # needed to prevent a cycle
serviceConfig = {
Type = "oneshot";
RemainAfterExit = true;
ExecStop = "${pkgs.runtimeShell} -c 'echo 1 > /sys/class/block/${dev}/reset'";
};
script = ''
set -u
set -o 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))
set -euo pipefail
echo $mem > /sys/class/block/${dev}/disksize
# Calculate memory to use for zram
mem=$(${pkgs.gawk}/bin/awk '/MemTotal: / {
print int($2*${toString cfg.memoryPercent}/100.0/${toString devicesCount}*1024)
}' /proc/meminfo)
${pkgs.utillinux}/sbin/zramctl --size $mem --algorithm ${cfg.algorithm} /dev/${dev}
${pkgs.utillinux}/sbin/mkswap /dev/${dev}
'';
restartIfChanged = false;
@ -111,6 +157,9 @@ 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" ];
unitConfig.DefaultDependencies = false; # needed to prevent a cycle
serviceConfig = {
Type = "oneshot";
RemainAfterExit = true;
@ -118,7 +167,11 @@ in
ExecStart = "${modprobe} zram";
ExecStop = "${modprobe} -r zram";
};
restartTriggers = [ cfg.numDevices ];
restartTriggers = [
cfg.numDevices
cfg.algorithm
cfg.memoryPercent
];
restartIfChanged = true;
})]);