Alexis HAUSER <alexis.hauser@telecom-bretagne.eu> writes:

...

Look for vramMultiplier in osinfo-defaults.properties file. The following formula applies: vram_size = vramMultiplier * vgamem You must restart Engine to apply the new setting.

The only thin I found about it in that file is : os.rhel_7x64.devices.display.vramMultiplier.value = 2

That's right. You can add similar lines for other OSes as needed.

I am not sure this file is what I want : from what it seems to only affects some parameters at the creation of the OS. i.e. if I take an ubuntu but I set it up as RHEL7, it won't have more vram.

Video RAM settings should be applied when a VM is started. So if you set your Ubuntu VM as RHEL7 and then start it, it should get 32 MB of vram (it works for me).

With centOS7 however (that I have set as RHEL7 at its creation), it has more vram, but not 2*, really more : centOS has : "vram_size=33554432" from what qemu says and all others VM have 8 instead of...33

If vramMultiplier is not present then a fixed value of 8 MB is used. If it is present then the formula above applies -- note that vgamem is 16 MB, so vram = 2 * 16 MB = 32 MB is indeed the expected value.

Alexis HAUSER <alexis.hauser@telecom-bretagne.eu> writes:

Is there a way to change it for all os in a row ? something like "os.all.devices.display.vramMultiplier.value = 2"

Try `os.other.devices.display.vramMultiplier.value'.

How is that memory used on the hypervisor ? Will this use the physical vram for the same amount or will it use the physical RAM ? i.e. if I set all VM to 32, can I reach the limit of the resources from my hypervisor quickly ?

It depends on how the video RAM is used in the guest OSes and their drivers. The allocated memory is unlikely to be used all immediately but it's available to the guest OS and it can use it for many different purposes, up to the amount you provided. So it's better not to set unnecessarily large video RAM values and limit them just to the amount needed (and that optimum value may differ for different OSes or even different versions or configurations of the same OS).

So basically, I must create a 01-defaults.properties file ? Will it ovewrite only parameters I change in that file, or will it totally replace the whole configuration with my new file ?

I think it should just add/override the specified parameters, not replace the whole configuration.