Gfilui

I have a swap file /swapfile of 1GB size in accordance with the procedure described in the ubuntu swap faq.

When doing a RAM intensive task, I use the "System Monitor" to check the load on my Memory and my Swap. When the task is done, the Memory load goes down quickly ... however, the Swap load stays high for a very long time and only trickles down very slowly (see image).

When calling sudo swapoff -a && swapon -a, I can clear the Swap manually ... but I'd rather know:

1. Why is Swap taking so long to be cleared?


2. Is this impacting the performance?

Short answer: if your computer is not acting very slowly, it's fine.

Linux will only get the contents out of swap if they are needed, otherwise, there's no point in loading something that isn't in use from swap into RAM, thereby reducing the cache.

A way to check if your system is being limited by swap is checking

vmstat 1

and looking at the wa column, which shows how long it takes before a process can run. Also, use a tool such as htop and see how many processes are in disk sleep(D).

Also, you should have a bit more swap. According to the SwapFAQ:

 RAM(MB) No hibernation With Hibernation Maximum
 256 256 512 512
 512 512 1024 1024
 1024 1024 2048 2048

 RAM(GB) No hibernation With Hibernation Maximum
 1 1 2 2
 2 1 3 4
 3 2 5 6
 4 2 6 8
 5 2 7 10
 6 2 8 12
 8 3 11 16
 12 3 15 24
 16 4 20 32
 24 5 29 48
 32 6 38 64
 64 8 72 128
 128 11 139 256

If you have 16GB of RAM, you should have between 4GB and 32GB