Sunday, September 29, 2013

How to Check and Modify Linux Kernel Performance on Linux RHEL / CentOS VM swap tuning

vm.swappiness is a tunable kernel parameter that controls how much the kernel favors swap over RAM. At the source code level, it’s also defined as the tendency to steal mapped memory. A high swappiness value means that the kernel will be more apt to unmap mapped pages. A low swappiness value means the opposite, the kernel will be less apt to unmap mapped pages. In other words, the higher the vm.swappiness value, the more the system will swap.

The default value I have seen on RHEL/CentOS/SLES  is 60.

To find out what the default value is on a particular server run this Command:

[root@station1 Documents]# sysctl vm.swappiness
vm.swappiness = 60

The value is also located in /proc/sys/vm/swappiness.

[root@station1 Documents]# cat /proc/sys/vm/swappiness
60

Note:  You can set the maximum value up to 100, the minimum is 0.

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