Zswap is a kernel feature which provides a compressed RAM cache for swap pages, it works in conjuction with swap space.
If swap partition is not present then we can create a swapfile and activate it.
Making a filebased swap,
Create a 2GB swap partition with “dd” and activate it.
[root@localhost cipher]# dd if=/dev/zero of=/mnt/swapfile bs=1024 count=2097152
2097152+0 records in
2097152+0 records out
2147483648 bytes (2.1 GB, 2.0 GiB) copied, 33.932 s, 63.3 MB/s
[root@localhost cipher]# chmod 600 /mnt/swapfile
[root@localhost cipher]# mkswap /mnt/swapfile
Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
no label, UUID=e0c85b8d-4d93-4475-a471-e6e7f47bbfd9
[root@localhost cipher]# swapon /mnt/swapfile
[root@localhost cipher]# free -h
total used free shared buff/cache available
Mem: 3.8G 1.4G 166M 113M 2.3G 2.1G
Swap: 2.0G 0B 2.0G
[root@localhost cipher]# free -h
total used free shared buff/cache available
Mem: 3.8G 1.4G 168M 112M 2.3G 2.1G
Swap: 2.0G 0B 2.0G
Add entries in fstab to make chnages persistent across reboot
# # /etc/fstab # Created by anaconda on Wed Nov 21 15:05:32 2018 # # Accessible filesystems, by reference, are maintained under '/dev/disk' # See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info # UUID=07187215-9cd6-4727-b753-596d69daf9d7 / ext4 defaults 1 1 /mnt/swapfile swap swap defaults 0 0
After the swap partiton setup now we can proceed with zswap configuration, zswap requires a compression algorithm to be set, we will be using lz4 compression method.
Enabling zswap at runtime.
# echo 1 > /sys/module/zswap/parameters/enabled
To enable zswap permanentaly use grub parameters “…zswap.enabled=1 zswap.max_pool_percent=25 zswap.compressor=lz4”
[root@localhost cipher]# cat /etc/default/grub GRUB_TIMEOUT=5 GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)" GRUB_DEFAULT=saved GRUB_DISABLE_SUBMENU=true GRUB_TERMINAL_OUTPUT="console" GRUB_CMDLINE_LINUX="rhgb quiet video=SVIDEO-1:d elevator=noop console=tty0 console=ttyS0,115200n8 zswap.enabled=1 zswap.max_pool_percent=25 zswap.compressor=lz4" GRUB_DISABLE_RECOVERY="true"
Updating grub configuration after making changes
#grub2-mkconfig -o /boot/grub2/grub.cfg
Set zswap to use 25% of the ram
# echo 25 > /sys/module/zswap/parameters/max_pool_percent
Enabling lz4 algorithm
#modprobe lz4 lz4_compress #cat /etc/dracut.conf.d/lz4.conf << EOF modprobe lz4 lz4_compress EOF
Regenerate initramfs images
[root@localhost cipher]# dracut --regenerate-all --force
Checking the current Zswap usagel,cheking if zswap is active.
[root@localhost cipher]# cat /sys/module/zswap/parameters/enabled Y [root@localhost cipher]# dmesg | grep -i zswap [ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.19.2-200.fc28.x86_64 root=UUID=07187215-9cd6-4727-b753-596d69daf9d7 ro rhgb quiet video=SVIDEO-1:d elevator=noop console=tty0 console=ttyS0,115200n8 zswap.enabled=1 zswap.max_pool_percent=25 zswap.compressor=lz4 [ 0.362239] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.19.2-200.fc28.x86_64 root=UUID=07187215-9cd6-4727-b753-596d69daf9d7 ro rhgb quiet video=SVIDEO-1:d elevator=noop console=tty0 console=ttyS0,115200n8 zswap.enabled=1 zswap.max_pool_percent=25 zswap.compressor=lz4 [ 1.820253] zswap: loaded using pool lz4/zbud [root@localhost cipher]# grep -R . /sys/module/zswap grep: /sys/module/zswap/uevent: Permission denied /sys/module/zswap/parameters/same_filled_pages_enabled:Y /sys/module/zswap/parameters/enabled:Y /sys/module/zswap/parameters/max_pool_percent:25 /sys/module/zswap/parameters/compressor:lz4 /sys/module/zswap/parameters/zpool:zbud