Thanks for your reply.

I can see that both CentOS 7 and CentOS 8 (Rocky 8/9) have the balloon modules:

CentOS 7:

$ find /usr/lib/modules/`uname -r` -iname "*balloon*"
/usr/lib/modules/3.10.0-1160.83.1.el7.x86_64/kernel/drivers/hv/hv_balloon.ko.xz
/usr/lib/modules/3.10.0-1160.83.1.el7.x86_64/kernel/drivers/virtio/virtio_balloon.ko.xz
/usr/lib/modules/3.10.0-1160.83.1.el7.x86_64/kernel/drivers/misc/vmw_balloon.ko.xz

Rocky 8:

$ find /usr/lib/modules/`uname -r` -iname "*balloon*"
/usr/lib/modules/4.18.0-477.21.1.el8_8.x86_64/kernel/drivers/virtio/virtio_balloon.ko.xz
/usr/lib/modules/4.18.0-477.21.1.el8_8.x86_64/kernel/drivers/hv/hv_balloon.ko.xz
/usr/lib/modules/4.18.0-477.21.1.el8_8.x86_64/kernel/drivers/misc/vmw_balloon.ko.xz

Maybe it is possible to manually load this module on system boot, but I have no idea how to do it, nor which one is the correct module for Xen. Do you have any clue?

Thanks!

I just installed a new VM with original CentOS 8 (not Rocky) and it behaves exact like happens on Rocky 8 and Rocky 9. Is anything I can do to fix this supposed issue with the ballooning driver of the kernel? Or is it anything that must be resolved inside XCP-ng code?

Thanks

As long Dynamic memory is Less or Equal Static, I AM ABLE to change it while VM is live to desired value (in this case, up to 16GB). The only case I have to halt the VM is to change the Static memory. So, in this case I have 16GB Static and 8GB Dynamic, I can live increase total memory up to 16GB (or reduce it) and CentOS 7 operating system recognize this memory change on the fly.

Please note that I'm just having the problem with Rocky 8, that shows 16GB of total RAM, even having limited Dynamic memory to 8GB. I'm able to decrease or increase Dynamic memory (up to 16GB set on Static), but the Rocky OS will always shows 16GB of total RAM.

This is the memory config for CentOS 7 VM

And this is the config for Rocky 8 VM

As you can see, they are exactly the same.
Thanks,

Hello.

I'm using XCP-ng version 8.2.1 and I have hundreds VMs running CentOS 7. I'm planing to migrate the Operating System of the VMs to Rocky Linux 8, due to EOL of CentOS 7 in a few months. However I'm facing a prohibitive issue on Rocky Linux 8 (and 9) about available memory on VM.

To explain the issue, let's assume I need a VM with 8GB of RAM, but I need to be able increase this memory without having to shutdown the VM, so I'm setting 8GB of Dynamic and 16GB of Static memory. The problem is that on CentOS 7, it shows the Dynamic amount as the total memory (8GB), but on CentOS 8 (or Rocky 8, o Rocky 9), the operating system shows the Static memory as total memory. Then the OS "thinks" that it have 16GB of memory available, but it only 8GB, causing the MV to reboot when OS tried to allocate memory over 8GB.

You guys can reproduce the problem issuing the following command at the Rocky 8 prompt:

</dev/zero head -c 15000m | tail

When doing this on CentOS 7 and the system reaches the total available RAM (8GB), then kernel is going to kill this process due to out of memory (OOM). In other hand, doing the same test on Rocky 8, the VM is going to reboot.

Free memory on CentOS 7:

$ free -m
              total        used        free      shared  buff/cache   available
Mem:           7419        2059        3044         227        2315        4806
Swap:          2047           0        2047

Free memory on Rocky 8:

$ free -m
              total        used        free      shared  buff/cache   available
Mem:          15738         178       15427           8         132       15327
Swap:          2047           0        2047

Note that on CentOS7 it shows about 8GB total RAM, while on Rocky 8 it shows about 16GB total RAM. Both VMs has exact the same memory configuration:
16GB Static
8GB Dynamic

Also, both VMs are using the latest guest utilities installed from EPEL repo:
xe-guest-utilities-latest-7.30.0-2.el7.x86_64 (for CentOS 7) and xe-guest-utilities-latest-7.30.0-3.el8.x86_64 (for Rocky 8).

Now, my questions are:

• is it a XCP-ng bug? or
• is it a xe-guest-utilities bug? or
• is it a Rocky 8 (or 9) bug? or
• is there anything I can do to solve it??

Thanks a lot!
Ivan Apolonio