Ubuntu Manpage: zram-generator.conf - Systemd unit generator for zram swap devices (configuration)

Provided by: systemd-zram-generator_1.2.1-2_amd64

NAME

       zram-generator.conf - Systemd unit generator for zram swap devices (configuration)

SYNOPSIS

       /usr/lib/systemd/zram-generator.conf
       /usr/local/lib/systemd/zram-generator.conf
       /etc/systemd/zram-generator.conf
       /run/systemd/zram-generator.conf

       /usr/lib/systemd/zram-generator.conf.d/*.conf
       /usr/local/lib/systemd/zram-generator.conf.d/*.conf
       /etc/systemd/zram-generator.conf.d/*.conf
       /run/systemd/zram-generator.conf.d/*.conf

DESCRIPTION

       These  files  configure  devices  created  by  zram-generator(8).  See  systemd.syntax(5)  for  a general
       description of the syntax.

CONFIGURATION DIRECTORIES AND PRECEDENCE

The default configuration doesn't specify any devices. Consult
/usr/share/zram-generator/zram-generator.conf.example for an example configuration file.

When packages need to customize the configuration, they can install configuration snippets in
/usr/lib/systemd/zram-generator.conf.d/. Files in /etc/ are reserved for the local administrator, who may
use this logic to override the configuration files installed by vendor packages. The main configuration
file is read before any of the configuration directories, and has the lowest precedence; entries in a
file in any configuration directory override entries in the single configuration file. Files in the
*.conf.d/ configuration subdirectories are sorted by their filename in lexicographic order, regardless of
which of the subdirectories they reside in. When multiple files specify the same option, for options
which accept just a single value, the entry in the file with the lexicographically latest name takes
precedence. It is recommended to prefix all filenames in those subdirectories with a two-digit number and
a dash, to simplify the ordering of the files.

To disable a configuration file supplied by the vendor, the recommended way is to place a symlink to
/dev/null in the configuration directory in /etc/, with the same filename as the vendor configuration
file.

The generator understands the following option on the kernel command-line: systemd.zram[=0|1]. When
specified with a true argument (or no argument), the zram0 device will be created. Default options apply,
but may be overridden by configuration on disk if present. When specified with a false argument, no zram
devices will be created by the generator. This option thus has higher priority than the configuration
files.

OPTIONS

Each device is configured independently in its [zramN] section, where N is a nonnegative integer. The
global section may contain DIRECTIVES. Other sections are ignored.

Devices with the final size of 0 will be discarded.

• host-memory-limit=

Sets the upper limit on the total usable RAM (as defined by MemTotal in /proc/meminfo, confer
proc(5)) above which the device will not be created.

This takes a nonnegative number, representing that limit in megabytes, or the literal string none,
which can be used to override a limit set earlier.

Defaults to none.

• zram-size=

Sets the size of the zram device as a function of MemTotal, available as the ram variable. Additional
variables may be provided by DIRECTIVES.

Arithmetic operators (^%/*-+), e, π, SI suffixes, log(), int(), ceil(), floor(), round(), abs(),
min(), max(), and trigonometric functions are supported.

Defaults to min(ram / 2, 4096).

• zram-resident-limit=

Sets the maximum resident memory limit of the zram device (or 0 for no limit) as a function of
MemTotal, available as the ram variable.

Same format as zram-size. Defaults to 0.

• compression-algorithm=

Specifies the algorithm used to compress the zram device.

This takes a whitespace-separated list string, representing the algorithms to use, and parameters in
parenteses.
Consult /sys/block/zram0/comp_algorithm (and .../recomp_algorithm) for a list of currently loaded
compression algorithms, but note that additional ones may be loaded on demand.

If unset, none will be configured and the kernel's default will be used.
If more than one is given, and recompression is enabled in the kernel, subsequent ones will be set as
the recompression algorithms, with decreasing priority.

If a compression algorithm is suffixed with a parenthesised comma-separated list of parameters, those
are given to .../algorithm_params (and .../recompress). A parenthesised parameter list without a
compression algorithm is set as the global recompression parameters.

• writeback-device=

Write incompressible pages, for which no gain was achieved, to the specified device under memory
pressure. This corresponds to the /sys/block/zramX/backing_dev parameter.

Takes a path to a block device, like /dev/disk/by-partuuid/2d54ffa0-01 or
/dev/zvol/tarta-zoot/swap-writeback.

If unset, none is used, and incompressible pages are kept in RAM.

• swap-priority=

Controls the relative swap priority, a value between -1 and 32767. Higher numbers indicate higher
priority.

If unset, 100 is used.

• mount-point=

Format the device with a file system (not as swap) and mount this file system over the specified
directory. When neither this option nor fs-type= is specified, the device will be formatted as swap.

Note that the device is temporary: contents will be destroyed automatically after the file system is
unmounted (to release the backing memory).

• fs-type=

Specifies how the device shall be formatted. The default is ext2 if mount-point is specified, and
swap otherwise. (Effectively, the device will be formatted as swap, if neither fs-type= nor
mount-point= are specified.)

Note that the device is temporary: contents will be destroyed automatically after the file system is
unmounted (to release the backing memory).

Also see systemd-makefs(8).

• options=

Sets mount or swapon options. Availability depends on fs-type.

Defaults to discard.

DIRECTIVES

       The global section (before any section header) may contain directives in the following form:

       •   set!variable=program

           program is executed by the shell as-if  by  system(3),  its  standard  output  stream  parsed  as  an
           arithmetic  expression  (like  zram-size/zram-resident-limit),  then  the  result  is remembered into
           variable, usable in later set!s and zram-sizes/zram-resident-limits.

ENVIRONMENT VARIABLES

       Setting   ZRAM_GENERATOR_ROOT   during   parsing   will   cause   /proc/meminfo   to   be    read    from
       $ZRAM_GENERATOR_ROOT/proc/meminfo                               instead,                              and
       {/usr/lib,/usr/local/lib,/etc,/run}/systemd/zram-generator.conf       to       be        read        from
       $ZRAM_GENERATOR_ROOT/{/usr/lib,/usr/local/lib,/etc,/run}/systemd/zram-generator.conf.

EXAMPLES

       The default configuration will yield the following:

            zram device size
                ^
                │
             4G>│               ooooooooooooo
                │             o
                │           o
                │         o
             2G>│       o
                │     o
                │   o
           512M>│ o
                0───────────────────────> total usable RAM
                  ^     ^       ^
                  1G    4G      8G

       A piecewise-linear size 1:1 for the first 4G, then 1:2 above, up to a max of 32G:
         zram-size = min(min(ram, 4096) + max(ram - 4096, 0) / 2, 32 * 1024)

            zram device size
                ^
            32G>|                                                oooooooooooooo
                |                                            o
            30G>|                                        o
                |
               /=/
                |
             8G>│                           o
                │                       o
                │                   o
                │               o
                │           o
             4G>│       o
                │     o
                │   o
             1G>│ o
                0───────────────────────────────────||──────────────────────> total usable RAM
                  ^     ^       ^               ^        ^       ^       ^
                  1G    4G      8G             12G      56G     60G     64G

OBSOLETE OPTIONS

       •   memory-limit=

           Compatibility alias for host-memory-limit.

       •   zram-fraction=

           Defines the scaling factor of the zram device's size with relation to the total usable RAM.

           This takes a nonnegative floating-point number representing that factor.

           Defaulted to 0.5. Setting this or max-zram-size overrides zram-size.

       •   max-zram-size=

           Sets the limit on the zram device's size obtained by zram-fraction.

           This  takes  a  nonnegative number, representing that limit in megabytes, or the literal string none,
           which can be used to override a limit set earlier.

           Defaulted to 4096. Setting this or zram-fraction overrides zram-size.

REPORTING BUGS

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