What is swappiness and how do I change it?

The swappiness parameter controls the logical functions of the kernel to forward processes out of physical memory and onto the swap. safe side caution : disks are much slower than RAM, this can lead to slower response times for system and applications if processes are too aggressively moved out of memory.

swappiness can have a value of between 0 and 100
swappiness=0 tells the kernel to avoid swapping processes out of physical memory for as long as possible
swappiness=100 tells the kernel to aggressively swap processes out of physical memory and move them to swap cache

The default setting in Ubuntu is swappiness=60. Reducing the default value of swappiness will probably improve overall performance for a typical Ubuntu desktop installation. A value of swappiness=10 is recommended, but feel free to experiment.

The Linux kernel provides a flexibility to set how we can control the swap file is used, called swappiness.

[email protected]:~$ cat /proc/sys/vm/swappiness
60

As I have 8 GB of RAM I would like to turn that down to 10 or 15. The swap file will then only be used when my RAM usage is around 80 or 90 percent. To change the system swappiness value, open /etc/sysctl.conf as root. Then, change or add this line to the file:

vm.swappiness = 10

Reboot the system for the change to take effect.

You can also change the value while your system is still in running mode using root shell :

sysctl vm.swappiness=10

You can also clear your swap by running swapoff -a and then swapon -a as root instead of rebooting to get the same effect.

To calculate your swap Formula:

free -m (total) / 100 = A

A * 20

[email protected]:/home/one# free -m
             total       used       free     shared    buffers     cached
Mem:          8192       2262       5930          0        389        865
-/+ buffers/cache:        903       3047
Swap:         8191          0       8191

so total is 8192 / 100 = 81.92 * 20 = 1638

So what it mean is that when 20% (1638 MB) out of 8192 memory is left then it will start using swap.

Source : help of ubuntu’s swapfaq

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