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turbo
Asked: 2011-08-12 02:01:51 +0800 CST

How to permanently enable compressed ram swap? What version to use?

  • 772

EDIT: In precise there's now zram-config. It's an upstart job compressing up to half of your ram spread over $(number of CPU cores) swap devices. It didn't allways start at boot but issuing sudo service zram-config start works.

I enabled compcache="256 M" in /etc/initramfs-tools/initramfs.conf as described here (by me :P). This - I believe - creates /dev/ramzswap0 but it is never enabled as swap. It works only after mkswap && swapon.

Then there is the module zram that creates /dev/zram. Is it something else? It works the same way but /dev/ramzswap is created from the module ramzswap.

At the end of the day I wanna have a compressed swap in ram and use the better of the two and for that I need to know how to enable it permanently in a non hackish way. How is this done?

I wrote about ramzswap in Lucid here but things have changed in Natty. You can still enable ramzswap in initramfs.conf but it doesn't get activated.

P.S.:I scanned all udev rules in /lib and/etc but found nothing of interest.

11.04

4 Answers

  1. I was struggling with the same problem.

    Today I found an excellent blog post about it. http://weirdfellow.wordpress.com/2011/05/04/compressed-ram-with-zram/

    Although "sudo start zramswap" didn't work, when I restarted my PC it solved my problem perfectly.

    Try it.

    • 2
  2. Best Answer

    There's now a PPA that installs a proper Upstart script for enabling zram at boot-time. It chooses the correct size and number of compressed swap devices for your system.

    https://launchpad.net/~shnatsel/+archive/zram

    • 2

  3. Straight from the Debian wiki. For me, this is the easiest.

    First, copy and paste this code into /etc/init.d/zram

    ### 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 protected]>
# 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

    Next, execute these two commands:

    sudo chmod +x /etc/init.d/zram
sudo /etc/init.d/zram start

    Finally, to add zram at startup:

    sudo update-rc.d zram defaults

    Done.

    • 2

  4. Here's the cheap solution. Add the following line to /etc/rc.local, before the exit 0:

    find /dev/ -maxdepth 1 -name 'ramzswap*' | while read dev; do
    mkswap $dev
    swapon -p 1000 $dev
done
    • 1