How to move swap back to RAM
Published: Aug 16, 2013 · Tags: Linux
This post explains how to move the data stored on the swap device/file back to RAM.
Let’s consider the following situation:
shell> free -m total used free shared buffers cached Mem: 7872 5938 1934 0 194 367 -/+ buffers/cache: 5376 2496 Swap: 3070 1318 1752
Here we have 1318M of data in the swap and 1934M of unused memory so moving back the data to RAM won’t affect the cached data.
shell> swapoff -a shell> swapon -a shell> free -m total used free shared buffers cached Mem: 7872 7122 750 0 194 370 -/+ buffers/cache: 6557 1315 Swap: 3070 0 3070
The amount of swap space used is now 0.
First, check you have enough free memory. This is very important because without the necessary amout of free memory, some running applications may encounter the wrath of the OOM Killer.
The amount of free RAM (1934M) is bigger than the concent of the swap space (1318) therefore the system will be able to swap out without triggering the OOM Killer and without trashing the cache. It is also correct to consider the amount free RAM “-/+ buffers/cache” but, in this case, you have to evaluate the impact of lowering the available cache on your system, before continuing.
Now here is the trick: disabling the swap space will force the kernel to move the content back to RAM. It can take some time, depending on the amount of data to read from the swap device. Once it is done, turn the swap back on.