zram-generator

/usr/lib/systemd/system-generators/zram-generator TARGET_DIR [2RGET_DIR 3RGET_DIR]
/usr/lib/systemd/system-generators/zram-generator --setup-device DEVICE
/usr/lib/systemd/system-generators/zram-generator --reset-device DEVICE

zram-generator is a generator that creates systemd units to format and use compressed RAM devices, either as swap or a mount point.

The generator will be invoked by systemd early at boot. The generator will then:

1.

read configuration files from {/etc,/lib}/systemd/zram-generator.conf[.d] (see zram-generator.conf(5) for details);

2.

generate systemd.swap(5) and/or systemd.mount(5) units into TARGET_DIR and connect them to swap.target or local-fs.target as appropriate;

3.

ensure the zram module is loaded and create the requested devices.

The generator does nothing if run inside a container (as determined by systemd-detect-virt(8) --container).

The generator also understands the kernel command-line option systemd.zram. See zram-generator.conf(5) for details.

Setting the ZRAM_GENERATOR_ROOT environment variable makes the generator run in test mode, in which case containerisation is ignored and step 3 is skipped.
For the ramifications of ZRAM_GENERATOR_ROOT on config handling, see zram-generator.conf(5).

Generated dev-zramN.swap units depend on systemd-swap-create@zramN.service, which will:

1.

read configuration files from {/etc,/lib}/systemd/zram-generator.conf[.d] (see zram-generator.conf(5) for details);

2.

set the desired compression algorithm, if any; if the current kernel doesn't understand the specified algorithm, a warning is issued, but execution continues;

3.

set the desired blockdev size and format it as swap with systemd-makefs(8).

Generated path-to-mount-point.mount units depend on systemd-swap-create@zramN.service. The effect is similar to what happens for swap units, but of course they are formatted with a file system.

When the unit is stopped, the zram device is reset, freeing memory and allowing the device to be reused.

zram-generator implements systemd.generator(7).

<https://github.com/systemd/zram-generator/issues>

zram-generator.conf(5), systemd.generator(7), systemd.swap(5)

<https://github.com/systemd/zram-generator>

Linux documentation of zram: <https://kernel.org/doc/html/latest/admin-guide/blockdev/zram.html>
and the zram sysfs ABI: <https://kernel.org/doc/Documentation/ABI/testing/sysfs-block-zram>