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

Provided by: systemd-zram-generator_1.2.1-1_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