How do I configure swappiness?

The Linux kernel provides a tweakable setting that controls how often the swap file is used, called swappiness.

A swappiness setting of zero means that the disk will be avoided unless absolutely necessary (you run out of memory), while a swappiness setting of 100 means that programs will be swapped to disk almost instantly.

Ubuntu system comes with a default of 60, meaning that the swap file will be used fairly often if the memory usage is around half of my RAM. You can check your own system's swappiness value by running:

one@onezero:~$ cat /proc/sys/vm/swappiness
60

As I have 4 GB of RAM I'd 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

Apply the change.

sudo sysctl -p

You can also change the value while your system is still running with:

sysctl vm.swappiness=10

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

To calculate your swap Formula:

free -m (total) / 100 = A

A * 10

root@onezero:/home/one# free -m
             total       used       free     shared    buffers     cached
Mem:          3950       2262       1687          0        407        952
-/+ buffers/cache:        903       3047
Swap:         1953          0       1953

so total is 3950 / 100 = 39.5 * 10 = 395

So what it mean is that when 10 % (395 MB) of ram is left then it will start using swap.

                                          Help . Ubuntu . Swap

                                           What is swappiness

The swappiness parameter controls the tendency of the kernel to move processes out of physical memory and onto the swap disk. Because 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 between 0 and 100.
  • swappiness=0:
    • Kernel version 3.5 and newer: disables swapiness.
    • Kernel version older than 3.5: avoids swapping processes out of physical memory for as long as possible.
  • swappiness=1:
    • Kernel version 3.5 and over: minimum swappiness without disabling it entirely.
  • swappiness=100:
    • Tells the kernel to aggressively swap processes out of physical memory and move them to swap cache.

See http://en.wikipedia.org/wiki/Swappiness.

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.

Example

Started using swap at 91%:

enter image description here As I have configured my system & vm to make use of RAM at 90%, at 90% there was no swapping.

After that I opened some applications like Firefox & Shutter, and it started swapping because RAM usage is above 90%.

Tags:

Swap

Memory Usage

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