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Add zram

What is zram?​

zram, formerly called compcache, is a Linux kernel module for creating a compressed block device in RAM, i.e., a RAM disk, but with on-the-fly "disk" compression. The block device created with zram can then be used for swap or as general-purpose RAM disk. - Wikipedia

Prerequisites​

Disable the Raspberry Pi OS swapfile:

sudo systemctl disable dphys-swapfile.service

Install zram​

Install the zram tools:

sudo apt install -y zram-tools

Open /etc/default/zramswap:

sudo nano /etc/default/zramswap

And update it as follows:

# Compression algorithm selection
# speed: lz4 > zstd > lzo
# compression: zstd > lzo > lz4
# This is not inclusive of all that is available in latest kernels
# See /sys/block/zram0/comp_algorithm (when zram module is loaded) to see
# what is currently set and available for your kernel[1]
# [1]  https://github.com/torvalds/linux/blob/master/Documentation/blockdev/zram.txt#L86
# ALGO=lz4

# Specifies the amount of RAM that should be used for zram
# based on a percentage the total amount of available memory
# This takes precedence and overrides SIZE below
PERCENT=150

# Specifies a static amount of RAM that should be used for
# the ZRAM devices, this is in MiB
# SIZE=256

# Specifies the priority for the swap devices, see swapon(2)
# for more details. Higher number = higher priority
# This should probably be higher than hdd/ssd swaps.
# PRIORITY=100

Then save (Ctrl+O) and exit (Ctrl+X) nano.

Reload zram:

sudo systemctl reload zramswap.service

Useful commands​

You can use the zramctl command to list the zram devices present and their status:

sudo zramctl

You should see something like:

NAME       ALGORITHM DISKSIZE  DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 lz4          11.4G  6.8G  4.1G  4.4G       4 [SWAP]

Run the following command to check your memory usage:

free -h

You should see something like:

               total        used        free      shared  buff/cache   available
Mem:           7.6Gi       7.4Gi        94Mi          0B       159Mi       132Mi
Swap:           11Gi       8.1Gi       3.4Gi

Resources​