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'''zram''' (previously called '''compcache''') can create RAM based block devices. It is an experimental (staging) module of the Linux kernel since 3.2. #language en
'''zram''' (previously called '''compcache''') can create RAM based compressed block devices. It is a module of the Linux kernel since 3.2.
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== Background information == If physical swap devices exist, they will also be used by the system, but with a lower priority than a Zram device.
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 * https://code.google.com/p/compcache/
 * http://en.wikipedia.org/wiki/Zram
See [[https://www.kernel.org/doc/html/latest/admin-guide/blockdev/zram.html|Linux zram documentation]] and WikiPedia:Zram for more info.
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== Startup script == Similar results as with Zram can be achieved with [[Zswap]], though Zswap needs a physical swap device (or swap file).
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Copy the following script to ''/etc/init.d/zram'': <<TableOfContents>>

== Automated setup ==

The packages DebianPackage:zram-tools and DebianPackage:systemd-zram-generator can be used to automatically setup zram devices.

=== zram-tools ===

DebianPackage:zram-tools is available since Debian buster.

It currently only sets up zram devices on systemd-based systems.

To allow up to 60% of the RAM to be used as a zstd compressed swap space:
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#!/bin/bash
### BEGIN INIT INFO
# Provides: zram
# Required-Start: $local_fs
# Required-Stop: $local_fs
# Default-Start: S
# Default-Stop: 0 1 6
# Short-Description: Use compressed RAM as in-memory swap
# Description: Use compressed RAM as in-memory swap
### END INIT INFO

# Author: Antonio Galea <antonio.galea@gmail.com>

FRACTION=75

MEMORY=`perl -ne'/^MemTotal:\s+(\d+)/ && print $1*1024;' < /proc/meminfo`
CPUS=`grep -c processor /proc/cpuinfo`
SIZE=$(( MEMORY * FRACTION / 100 / CPUS ))

case "$1" in
  "start")
    param=`modinfo zram|grep num_devices|cut -f2 -d:|tr -d ' '`
    modprobe zram $param=$CPUS
    for n in `seq $CPUS`; do
      i=$((n - 1))
      echo $SIZE > /sys/block/zram$i/disksize
      mkswap /dev/zram$i
      swapon /dev/zram$i -p 10
    done
    ;;
  "stop")
    for n in `seq $CPUS`; do
      i=$((n - 1))
      swapoff /dev/zram$i
    done
    sleep .5
    modprobe -r zram
    ;;
  *)
    echo "Usage: `basename $0` (start | stop)"
    exit 1
    ;;
esac
sudo apt install zram-tools
echo -e "ALGO=zstd\nPERCENT=60" | sudo tee -a /etc/default/zramswap
sudo service zramswap reload
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then instruct you system to start it at boot time, with the command ==== sysvinit ====

zram-tools [[DebianBug:960524|does not yet support sysvinit systems]] but there is an [[https://bugs.debian.org/cgi-bin/bugreport.cgi?att=1;bug=960524;filename=zramswap;msg=10|init script]] available. Download it and save it to ''/etc/init.d/zramswap'', then make the script executable and then instruct your system to start it at boot time:
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  insserv zram sudo chmod +x /etc/init.d/zramswap
sudo apt install insserv
sudo insserv zramswap
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=== systemd-zram-generator ===

systemd-zram-generator integrates zram devices into systemd using generated swap (and ext2 mount) units. This allows managing them individually with `systemctl` when desired.

== Manual setup ==

DebianMan:zramctl from DebianPackage:util-linux can list the zram devices present and their status and control them.

{{{
$ sudo zramctl
NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 lz4 4G 2.1G 248.6M 260.4M 8 [SWAP]
}}}

zram (previously called compcache) can create RAM based compressed block devices. It is a module of the Linux kernel since 3.2.

If physical swap devices exist, they will also be used by the system, but with a lower priority than a Zram device.

See Linux zram documentation and Zram for more info.

Similar results as with Zram can be achieved with Zswap, though Zswap needs a physical swap device (or swap file).

Automated setup

The packages zram-tools and systemd-zram-generator can be used to automatically setup zram devices.

zram-tools

zram-tools is available since Debian buster.

It currently only sets up zram devices on systemd-based systems.

To allow up to 60% of the RAM to be used as a zstd compressed swap space:

sudo apt install zram-tools
echo -e "ALGO=zstd\nPERCENT=60" | sudo tee -a /etc/default/zramswap
sudo service zramswap reload

sysvinit

zram-tools does not yet support sysvinit systems but there is an init script available. Download it and save it to /etc/init.d/zramswap, then make the script executable and then instruct your system to start it at boot time:

sudo chmod +x /etc/init.d/zramswap
sudo apt install insserv
sudo insserv zramswap

systemd-zram-generator

systemd-zram-generator integrates zram devices into systemd using generated swap (and ext2 mount) units. This allows managing them individually with systemctl when desired.

Manual setup

zramctl from util-linux can list the zram devices present and their status and control them.

$ sudo zramctl
NAME       ALGORITHM DISKSIZE  DATA  COMPR  TOTAL STREAMS MOUNTPOINT
/dev/zram0 lz4             4G  2.1G 248.6M 260.4M       8 [SWAP]