Update 02.03.2015: added (modified) Centos / Redhat:
A successor to compcache is zram which is fully integrated in the Linux kernel since 22.214.171.124 and uses lzo compression. The idea behind it is to create swap devices made of chunks of the ram and to compress those chunks on the fly to increase the available space used and ideally reduce the need of swapping to slow disks.
It uses a small extra amount of the CPU, however, the reduced i/o usage should more than make up for this. This is primarily interesting for a small scaled VPS, Netbooks or low memory devices. Also virtualisation hosts should benefit of compressed memory.
Unfortunatly the zram-config script is currently not part of the Debian and Centos distributions. I will run some further tests and update here.
In Ubuntu, from 12.04 onwards, the install script is included and it takes only a minute to setup zram.
How to setup in Ubuntu:
sudo apt-get install zram-config
# cat /proc/swaps Filename Type Size Used Priority /dev/zram0 partition 482900 0 5 /dev/zram1 partition 482900 0 5 /dev/zram2 partition 482900 0 5 /dev/zram3 partition 482900 0 5 # free -h total used free shared buffers cached Mem: 3.7G 2.6G 1.1G 255M 46M 1.0G -/+ buffers/cache: 1.5G 2.2G Swap: 1.8G 0B 1.8G
In the above case, I haven’t had any swap configured prior to using zram.
There are also guides for Debian and Centos/RedHat but they involve bit more work and use external scripts.
Debian 7 / Proxmox:
This is taken from here… https://wiki.debian.org/ZRam
vi /etc/init.d/zram #insert #!/bin/sh ### 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 <email@example.com> # Thanks to Przemysław Tomczyk for suggesting swapoff parallelization 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 && echo "disabled disk $n of $CPUS" & done wait sleep .5 modprobe -r zram ;; *) echo "Usage: `basename $0` (start | stop)" exit 1 ;; esac
You have to make the script executable:
chmod +x /etc/init.d/zram
Then instruct your system to start it at boot time, with the command
To test it:
Before: # free -h total used free shared buffers cached Mem: 2.0G 1.1G 841M 0B 336K 127M -/+ buffers/cache: 1.0G 969M Swap: 2.4G 0B 2.4G # cat /proc/swaps Filename Type Size Used Priority /dev/zd0 partition 2490364 0 -1
# cat /proc/swaps Filename Type Size Used Priority /dev/zd0 partition 2490364 0 -1 /dev/zram0 partition 1534428 0 10 # free -h total used free shared buffers cached Mem: 2.0G 675M 1.3G 0B 776K 60M -/+ buffers/cache: 614M 1.4G Swap: 3.8G 0B 3.8G
CentOS / Redhat:
Some sources state that you need Kernel version 126.96.36.199 or better compiled with zram module.
However, my CentOS 6.6 has 2.6.32-504.8.1.el6.x86_64 and it seems to work fine there too.
You can test that prerequisite by using:
If it doesn’t complain (return an error) you should be good to go.
For CentOS / RedHat install guide, I refer either to a guide from extremeshock. https://extremeshok.com/5094/centos-6-x-rhce-6-redhat-6-zram-compression-compressed-swap-residing-in-ram-over-allocating-memory/
Both ways worked flawless under CentOS 6.x and 7.x However, I had to reboot to get it really going.