Linux Desktop Hacks

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Chapter 10, Kernel

#91 Tweak Your Kernel Without Recompiling

HACK

desktop. If you’re running one of the later 2.6 kernels, this pack of hacks

includes a few tricks you can use to modify the performance of the kernel

you already have installed and running.

One of the most hotly debated performance topics is how Linux should

determine what memory to swap to disk, how much it should swap, and

when to do it. The answer is simple. Use one or more of the following

tweaks to control this process yourself.

Setting Swappiness via /proc

A kernel parameter is available that is represented as a pseudofile called /proc/

sys/vm/swappiness. The default value for the parameter is 70. You can log in

and view the default value with this command:

# cat /proc/sys/vm/swappiness

70

The number is a rough gauge for how likely it is that Linux will swap to disk

whatever it considers to be swappable. If you set it to 100, it will swap most

aggressively. If you set it to 20, it will tend to swap a lot less. Here is how

you can set it to either value (logged in as root):

# echo "100" > /proc/sys/vm/swappiness

# cat /proc/sys/vm/swappiness

100

# echo "20" > /proc/sys/vm/swappiness

# cat /proc/sys/vm/swappiness

20

The argument for either side goes like this. Set the swappiness value to a

high number, even to 100, if you run several bloated applications and do not

often switch between them. The end result will be that when you do ...