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Editor: ?AntonioGalea
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Deletions are marked like this. Additions are marked like this.
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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 == See https://code.google.com/p/compcache/ and WikiPedia:Zram for more info.
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 * https://code.google.com/p/compcache/
 * http://en.wikipedia.org/wiki/Zram
== Installation and use ==
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== Startup script == Starting at buster (released July 2019) it's possible to simply install the '''zram-tools''' package, customize '''/etc/default/zramswap''' for your needs.
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Copy the following script to ''/etc/init.d/zram'': It will create RAM based compressed swap device eliminating need for physical swap device. If physical swap device exist, it will also be used by the system, but with a lower priority than a Zram device.

Similar results as with Zram can be achieved with [[https://wiki.debian.org/Zswap|Zswap]], though Zswap needs a physical swap device (or swap file).

Install Zram and allow up to 60% of the RAM to be used as a zstd compressed swap space:
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#!/bin/bash sudo apt install zram-tools
echo -e "ALGO=zstd\nPERCENT=60" | sudo tee -a /etc/default/zramswap
systemctl reload zramswap.service
}}}

For systems using a standard SysV-based init system, it's possible to copy the following script to ''/etc/init.d/zram'':
{{{

#! /bin/sh
# Author: Antonio Galea <antonio.galea@gmail.com>
#
# Thanks to Przemysław Tomczyk for suggesting swapoff parallelization
# Distributed under the GPL version 3 or later, see terms at
# https://gnu.org/licenses/gpl-3.0.txt
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# Description: Use compressed RAM as in-memory swap  # Description: Use compressed RAM as in-memory swap
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# Author: Antonio Galea <antonio.galea@gmail.com>
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MEMORY=`perl -ne'/^MemTotal:\s+(\d+)/ && print $1*1024;' < /proc/meminfo`
CPUS=`grep -c processor /proc/cpuinfo`
SIZE=$(( MEMORY * FRACTION / 100 / CPUS ))
MEMORY=$(perl -ne '/^MemTotal:\s+(\d+)/ && print $1*1024' < /proc/meminfo)
CPUS=$(nproc)
SIZE=$((MEMORY * FRACTION / 100 / CPUS))
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  "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
    ;;
    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 --priority 10
        done
    
;;
    stop)
    
for n in $(seq $CPUS)
        do
      
i=$((n - 1))
       swapoff /dev/zram$i && echo "zram: disabled disk $n of $CPUS" &
        done

        wait
    
sleep .5
        modprobe --remove zram
    
;;
    *)
     echo "Usage: $(basename $0) (start | stop)"
        exit 1
     ;;
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# End of file
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then instruct you system to start it at boot time, with the command then make the script executable:
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  insserv zram chmod +x /etc/init.d/zram
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then instruct your system to start it at boot time, with the command (skip this on systemd)
{{{
apt-get install insserv
insserv zram
}}}

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

See https://code.google.com/p/compcache/ and Zram for more info.

Installation and use

Starting at buster (released July 2019) it's possible to simply install the zram-tools package, customize /etc/default/zramswap for your needs.

It will create RAM based compressed swap device eliminating need for physical swap device. If physical swap device exist, it will also be used by the system, but with a lower priority than a Zram device.

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

Install Zram and 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
systemctl reload zramswap.service

For systems using a standard SysV-based init system, it's possible to copy the following script to /etc/init.d/zram:

# Author: Antonio Galea <antonio.galea@gmail.com>
#
# Thanks to Przemysław Tomczyk for suggesting swapoff parallelization
# Distributed under the GPL version 3 or later, see terms at
# https://gnu.org/licenses/gpl-3.0.txt

### 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

FRACTION=75
MEMORY=$(perl -ne '/^MemTotal:\s+(\d+)/ && print $1*1024' < /proc/meminfo)
CPUS=$(nproc)
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 --priority 10
        done
        ;;
    stop)
        for n in $(seq $CPUS)
        do
            i=$((n - 1))
            swapoff /dev/zram$i && echo "zram: disabled disk $n of $CPUS" &
        done

        wait
        sleep .5
        modprobe --remove zram
        ;;
    *)
        echo "Usage: $(basename $0) (start | stop)"
        exit 1
        ;;
esac

# End of file

then make the script executable:

chmod +x /etc/init.d/zram

then instruct your system to start it at boot time, with the command (skip this on systemd)

apt-get install insserv
insserv zram