High SWAP usage eventhough plenty of RAM is available

[John4782]

Hello everyone,

I recently configured Proxmox VE 5.1 as my new hypervisor.
Everything works fine, but I can't explain its high SWAP usage.

Some more information about the system:

root@prxsrv:~# pveversion -v
proxmox-ve: 5.1-25 (running kernel: 4.13.4-1-pve)
pve-manager: 5.1-35 (running version: 5.1-35/722cc488)
pve-kernel-4.13.4-1-pve: 4.13.4-25

(long list omitted)

root@prxsrv:~# free -m
              total        used        free      shared  buff/cache   available
Mem:         128832       44071         994         136       83766       83572
Swap:          8191        7610         581

root@prxsrv:~# cat /proc/swaps
Filename                                Type            Size    Used    Priority
/dev/dm-1                               partition       8388604 7792752 -1

I can confirm that most of the Swap usage comes from the kvm process of one of my VMs:

root@prxsrv:~# cat /proc/16210/status | grep Swap
VmSwap:  7118964 kB

I have tried reducing the swappiness to 10 from 60 (perhaps 1 would do the trick?) and re-enabling the swap.
This has dramatically reduced Swap usage for two days, but then it steadily climbed back up to its current state (92%).

The VM has its own swap partition, which it abstains from completely. It is just the hypervisor that swaps a lot of memory.

This is obviously not a major problem, but it still gives me an itch, considering how much free RAM the machine has. I would also prefer not disabling it entirely.


Thanks a lot in advance

 

[ErikL]

We reduced the swappiness to 1, so it only uses swap space when RAM is full—works for us.
You should benchmark if this actually does any good for your setup.

 

[Rhinox]

Why do you keep swap, when you have plenty of RAM available? Honestly, I consider swap a thing of past, something of prehistoric computer age, when you had to pay a few thousand $ for 16MB RAM...

 

[John4782]

Thank you for your replies.

I changed the swappiness to 1 and the Swap usage does not go beyond 60%.
That is still considerably higher than I was hoping for, but it is less worrying than 99% usage.

I think in order to further influence SWAP usage, without disabling it althogether, I need to look at the type of load the individual VMs are processing. Considering that a custom project runs on it, it is not unlikely that it doesn't handle RAM efficiently and hence the hypervisor swaps frequently; to free up idle RAM address space.

The main reason I made this thread was because I was hoping there would be some mechanism unknown to me, which might be causing this kind of behaviour.

Given that this seems to be more of a Linux-related issue and not Proxmox itself, this thread may be closed.