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| See https://code.google.com/p/compcache/ and WikiPedia:Zram for more info. | 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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| == Installation and use == | 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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| Starting at buster (released July 2019) it's possible to simply install the '''zram-tools''' package, customize '''/etc/default/zramswap''' for your needs. | Similar results as with Zram can be achieved with [[Zswap]], though Zswap needs a physical swap device (or swap file). |
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| 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. | <<TableOfContents>> |
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| 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). | == Automated setup == |
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| Install Zram and allow up to 60% of the RAM to be used as a zstd compressed swap space: | 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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| systemctl reload zramswap.service | sudo service zramswap reload |
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| For systems using a standard SysV-based init system, it's possible to copy the following script to ''/etc/init.d/zram'': | ==== 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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#! /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 ### 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 |
sudo chmod +x /etc/init.d/zramswap sudo apt install insserv sudo insserv zramswap |
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| then make the script executable: | === 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. |
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| chmod +x /etc/init.d/zram | $ sudo zramctl NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT /dev/zram0 lz4 4G 2.1G 248.6M 260.4M 8 [SWAP] |
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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.
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]