Controlling the aggressiveness of swap

(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at: lawrence@krubner.com, or follow me on Twitter.

Interesting:

sysctl is similar ulimit: It allows to configure kernel parameters at runtime. If you wish to keep settings persistent across reboots you should edit /etc/sysctl.conf – be aware that wrong settings may break things in unforeseen ways.

Code Listing 4: Exploring sysctl variables
# sysctl -a
…
vm.swappiness = 60
…

The list of variables is quite long (367 lines on my system), but I picked out vm.swappiness here. It controls how aggressive swapping will be, the higher it is (with a maximum of 100) the more swap will be used. This can affect performance a lot on systems with little memory, depending on load and other factors.

Code Listing 5: Reducing swappiness
# sysctl vm.swappiness=0
vm.swappiness = 0

The effects of changing this setting are usually not felt instantly. But you can change many settings, especially network-related, this way. For servers this can offer a nice performance boost, but as with ulimit careless usage might cause your system to misbehave or slow down. If you don’t know what a variable controls, you should not modify it!

Post external references

  1. 1
    http://www.linuxhowtos.org/Tips%20and%20Tricks/ulimit.htm
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