Tuesday, June 14, 2016

Linux: Flush SWAP memory pages to RAM

On my dev machine, after I had started some services like Samba, MySQL, Jetty and executing some batch SQL queries which churned out a big database, I realized that my system had become slow and sluggish. I immediately checked the RAM usage via the System Task Monitor that comes with CentOS. And I noticed that though my RAM had substantial free space, SWAP was in action.

 If you ever run into such situation you can run the following commands to free you SWAP and move the active pages from SWAP to RAM. Before running the following commands ensure that you have substantial free space in your RAM i.e. free RAM size > SWAP memory size in use.

[root@paragcentosvm ~]# sudo swapoff -a
[root@paragcentosvm ~]# sudo swapon -a
The first command, swapoff, will take some time around 2-3 minutes (or more depending on the amount of SWAP memory in use, which needs to be freed). What is does is disables the SWAP partition for paging and swapping. When the -a flag is given, swapping is disabled on all known swap devices and files (as found in /proc/swaps or /etc/fstab)

The next swapon commands enables the SWAP partition for paging and swapping.

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