Best performance with zram expansion

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Notice: Update this article to correct some inaccurate information.

ZRAM expansion is the best option for expanding memory for Linux systems that for lower performance Cortex-A53 series within 1 GiB system memory.

How to activate ZRAM low performance systems as like Cortex-A53

A bah script file for ZRAM, zram.sh is here,

#!/bin/bash
export LANG=C
export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
if [ "$1" == --help ] || [ "$1" == -h ];then
  echo -e "This is a script made by Botspot to increase usable RAM by setting up ZRAM.
ZRAM uses compression to fit more memory in your available RAM.
This script will setup a ZRAM swapspace that is 4 times larger than usable RAM.
It also configures high-speed RAM-based file-storage at /zram.
Usage:
sudo zram.sh               Setup zram-swap and storage (if enabled)
sudo zram.sh stop          Disable all ZRAM devices and exit
sudo zram.sh storage-off   Disable the file-storage at /zram on next run
sudo zram.sh storage-on    Enable the file-storage at /zram on next run
zram.sh --help, -h         Display this information and exit"
  exit 0
fi
if [ $(id -u) -ne 0 ]; then
  echo "$0 must be run as root user"
  exit 1
fi
#avoid creating /zram storage if storage-off flag passed
if [ "$1" == storage-off ]; then
  #retain this flag for next boot
  if ! grep -qxF "ExecStart=/usr/bin/zram.sh storage-off" /etc/systemd/system/zram-swap.service ;then
    sed -i "s+^ExecStart=/usr/bin/zram.sh$+ExecStart=/usr/bin/zram.sh storage-off+g" /etc/systemd/system/zram-swap.service
  fi
  echo -e "zram.sh will not set up file-storage at /zram from now on."
#the /zram storage can be re-enabled with storage-on flag
elif [ "$1" == storage-on ]; then
  sed -i "s+^ExecStart=/usr/bin/zram.sh storage-off$+ExecStart=/usr/bin/zram.sh+g" /etc/systemd/system/zram-swap.service
  echo -e "zram.sh will set up file-storage at /zram from now on."
fi
# Load zram module
if ! lsmod | awk "{print $1}" | grep -qxF zram ;then
  if ! modprobe zram ;then
    echo "Failed to load zram kernel module"
    exit 1
  fi
fi
# disable all zram devices
echo -n "Disabling zram... "
IFS=$'\n'
for device_number in $(find /dev/ -name zram* -type b | tr -cd "0123456789\n") ;do
  #if zram device is a swap device, disable it
  swapoff /dev/zram${device_number} 2>/dev/null
  #if zram device is mounted, unmount it
  umount /dev/zram${device_number} 2>/dev/null
  #remove device
  echo $device_number >/sys/class/zram-control/hot_remove
done
echo Done
rm -rf /zram
#exit script now if "exit" flag passed
if [ "$1" == stop ]; then
  exit 0
fi
#create new zram drive - for swap
drive_num=$(cat /sys/class/zram-control/hot_add)
# use zstd compression if available - best option according to https://linuxreviews.org/Comparison_of_Compression_Algorithms#zram_block_drive_compression
if cat /sys/block/zram${drive_num}/comp_algorithm | grep -q zstd ;then
  algorithm=zstd
else
  algorithm=lz4
fi
echo $algorithm > /sys/block/zram${drive_num}/comp_algorithm
totalmem=$(free | grep -e "^Mem:" | awk '{print $2}')
#create zram disk 4 times larger than usable RAM - compression ratio for zstd can approach 5:1 according to https://linuxreviews.org/Zram
echo $((totalmem * 1024 * 4)) > /sys/block/zram${drive_num}/disksize
#make the swap device (by default this will be /dev/zram0)
mkswap /dev/zram${drive_num}
swapon /dev/zram${drive_num} -d -p 1
#create second zram drive: for temporary user-storage at /zram
if ! grep -qxF "ExecStart=/usr/bin/zram.sh storage-off" /etc/systemd/system/zram-swap.service ;then
  echo "Setting up ZRAM-powered file storage at /zram"
  #create new zram drive
  drive_num=$(cat /sys/class/zram-control/hot_add)
  # set compression algorithm
  echo $algorithm > /sys/block/zram${drive_num}/comp_algorithm
  #set the size of drive to be 4 times the available RAM
  echo $((totalmem * 1024 * 4)) > /sys/block/zram${drive_num}/disksize
  #create a partition and mount it
  mkfs.ext4 /dev/zram${drive_num} >/dev/null
  mkdir -p /zram
  mount /dev/zram${drive_num} /zram
  chmod -R 777 /zram #make writable for any user
fi

And put, or write script to /usr/bin with permission executable as like chmod 775.

Enable ZRAM swap

  1. Required zram module and zramctl must be pre-installed on Linux system (non-installable from apt).
  2. Disable dphy or swap from file.
    sudo /usr/sbin/dphys-swapfile uninstall or sudo systemctl disable mkswap.service.
  3. And make swap service to be disabled by ..
    sudo systemctl mask dphys-swapfiles.service or sudo systemctl mask mkswap.service
  4. Enable ZRAM swap
    sudo enable_module zram
  5. Make zram.sh in /usr/bin with upper content, and make it runnable with sudo chmod 775 /usr/bin/zram.sh.
  6. Make zram service script with this content in /etc/systemd/system/zram-swap.service.

/etc/systemd/system/zram-swap.service

[Unit]
Description=Configures zram swap device
After=local-fs.target

[Service]
Type=oneshot
ExecStart=/usr/bin/zram.sh
ExecStop=/usr/bin/zram.sh stop
RemainAfterExit=yes

[Install]
WantedBy = multi-user.target

Add these lines in /etc/sysctl.conf

# ZRAM configuration
vm.swappiness=100
vm.vfs_cache_pressure=500
vm.dirty_background_ratio=1
vm.dirty_ratio=50

This setting is recommended for zram the best performance.

Some trick for slower systems

ZRAM algorithm zstd is the best compression but slower than lz4 and lzo. You can update zram.sh script to select lz4 first then lzo, later for std from line 60 to …

if cat /sys/block/zram${drive_num}/comp_algorithm | grep -q lz4 ;then
  algorithm=lz4
elif cat /sys/block/zram${drive_num}/comp_algorithm | grep -q lzo ;then
  algorithm=lzo
else
  algorithm=zstd
fi

 

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