Hello Donagh,
                         memory size  e.g. 62000MB is the memory the VM tells the O/S is available you should be able to see how much is actually used if the agent is installed.
                          maximum memory e.g. 248000MB is the amount you can hot-plug for the VM otherwise you need to restart the VM to increase memory.
                          physical memory guaranteed e.g. 31000MB is the amount of memory the VM will have even if the balloon driver is activated.

The VMs will use memory as required, you can see how much memory they are actually using, also how much shared memory are the hosts using and how much is available to schedule new VMs?


Regards,
                 Paul S.
From: donagh.moran@oracle.com <donagh.moran@oracle.com>
Sent: 10 December 2019 10:04
To: users@ovirt.org <users@ovirt.org>
Subject: [ovirt-users] Clusters: Clarification needed on the ballooning memory feature and its affects on the physical hosts memory
 
Hi

For test purposes I'm configuring cluster with ballooning enabled and memory over-commit set to 200% with one host (total memory 128600 MB) connected. I then create 4 linux based VM's and I set the following on each: memory size: 62000MB, max memory: 248000MB (default value set when memory size is set) and a guaranteed memory value of 31000MB (default value set when memory size is set).

This all works as expected, I can start 4 VM's with a total memory size that double the physical memory available on the host. What I don't understand is when I view the general info on my host I see that the available memory is much higher than expected. Physical Memory:128600 MB total, 11574 MB used, 117026 MB free.

When researching the set up required to test this feature I came across this post https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.ovirt.org%2Fpipermail%2Fusers%2F2017-October%2F084675.html&amp;data=02%7C01%7Cp.staniforth%40leedsbeckett.ac.uk%7C3f6fe3e41c434eaa268808d77d58b65e%7Cd79a81124fbe417aa112cd0fb490d85c%7C0%7C0%7C637115692286198137&amp;sdata=x3r%2Bwz%2FM8CvwE7JIk5LBypnKMjxIwY8oDvDTdB8wM4c%3D&amp;reserved=0. It states the hosts memory load needs to exceed 80%. I was hoping that the allocation of physical memory to each VM would satisfy this condition but I am not sure it does. I have a few questions on this

Should setting the physical memory to each VM would satisfy the greater than 80% conditions?
Given we have guaranteed memory for each VM of 31000MB should the total of 124000Mb exceed the free memory on the host?
Does the hosts used physical memory only represent each VM's disk 4Gb virtual size?
Will the hosts free memory only decrease as the VM's consume storage?

Any clarification on the above questions would be most appreciated.

Regards
Donagh
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