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

Provided by: systemd-zram-generator_1.1.2-3_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. 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.

           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).

       ○   compression-algorithm=

           Specifies the algorithm used to compress the zram device.

           This takes a literal string, representing the algorithm to use.
           Consult  /sys/block/zram0/comp_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.

       ○   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.

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