4.4 and memory usage

[stefws]

Under Memory at https://HOST:8006/pve-docs/chapter-qm.html#qm_memory it's written:

'When allocating RAMs to your VMs, a good rule of thumb is always to leave 1GB of RAM available to the host'

But I tent to find that when getting at around 60% memory usage on a hypervisor host it start to send pages to swap. Anyway to avoid that until at a higher usage?

 

[spirit]

try to reduce swapiness
"echo 'vm.swappiness = 15' >> /etc/sysctl.conf"


(personnaly I don't have any swap partition on my hosts)

 

[AhmedF]

The Linux kernel provides a tweakable setting that controls how often the swap file is used, called swappiness

A swappiness setting of zero means that the disk will be avoided unless absolutely necessary (you run out of memory), while a swappiness setting of 100 means that programs will be swapped to disk almost instantly.

Ubuntu system comes with a default of 60, meaning that the swap file will be used fairly often if the memory usage is around half of my RAM. You can check your own system's swappiness value by running:

root@ahmed:~# cat /proc/sys/vm/swappiness
60
root@ahmed:~#

you can change the system swappiness value, open /etc/sysctl.conf as root. Then, change or add this line to the file:

vm.swappiness = 10

Reboot for the change to take effect

You can also change the value while your system is still running

sysctl vm.swappiness=10

 

[stefws]

Currently swap is off w/swappiness=0 so assume to ought to avoid swapping out pages at all.

At what levels are people allocating host memory for VM usage while remembering to be able to migrate VMs from a downed/upgrading host?

 

[AhmedF]

I don't think having swappiness set to zero is a good idea as node kernel will start sending OOM to kill application to preserve any needed memory , I usually set it to 10 to minimize swap paging and yes I usually allocate 1 GB of memory for the node itself and allocate the rest the VMs/CTs

 

[stefws]

Have add vm.swappiness = 0 to /etc/sysctl.d/pve_local.conf because I've read this note from IBM

 

[fireon]

We have also on all us Servers "vm.swappiness = 0".

 

[mjw]

I checked the tuned profiles that Red Hat distributes in their systems. The profiles "virtual-guest" and "virtual-host" both use vm.swappiness=10. According to this the PVE installer should use a lower default value than 60 (which is the Debian default).

 

[fireon]

I checked the tuned profiles that Red Hat distributes in their systems. The profiles "virtual-guest" and "virtual-host" both use vm.swappiness=10. According to this the PVE installer should use a lower default value than 60 (which is the Debian default).

I agree.