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Performance tuning Linux Kernel with swappiness parameter

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

To check the swappiness value use command: cat /proc/sys/vm/swappiness

To make a change permanent, edit the configuration file with your favorite editor:

vi /etc/sysctl.conf
and add following parameter to the end of the file like so:
Save the file and reboot.

Still, there are users who insist that, for example, a system backup should never force OpenOffice out to disk. They don't care how quickly a system maintenance application runs at 3:00 in the morning, but they care a lot about how the system responds when they are at the keyboard. This wish was expressed repeatedly until Andrew Morton exclaimed:
I'm gonna stick my fingers in my ears and sing "la la la" until people tell me "I set swappiness to zero and it didn't do what I wanted it to do.


Anonymous said...

' sysctl -p ' as root will load the settings, so, if you make changes, a reboot is not needed.

see the manpage for sysctl.

Janu "roxsku" Saksa said...

No, "sysctl -p" will reload values from ie. /proc/..../vm.swappiness in memory, but after that checking /etc/sysctl.conf it was NOT there (`uname -a` says "Linux raippa 2.6.26-2-686 #1 SMP Mon Aug 30 07:01:57 UTC 2010 i686 GNU/Linux" and it's Debian Lenny... Only way to have it working after boot really is to modify sysctl.conf by myself all other tests are temporary.

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