Hyper-V dynamic memory not correctly assigning more memory

Question

So, I got an alert from our monitoring system that there's less than 15% memory free on a virtual machine. I log in to investigate, it turns out that the VM in question is a Hyper-V VM with Dynamic Memory configured, running on Windows Server 2012 (not R2). The host is also Windows Server 2012 (not R2).

Looking in Hyper-V manager I can see the following under the "Memory" tab:

Startup Memory: 2048 MB
Dynamic Memory: Enabled
Minimum Memory: 512 MB
Maximum Memory: 8192 MB
Assigned Memory: 2826 MB [Plenty of opportunity to expand]
Memory Demand: 2769 MB
Memory Status: Low

Looking inside the guest, I see the following using Task Manager:

In use: 3.2 GB
Available: 483 MB
Committed: 3.6/6.2 GB
Cached: 410 MB
Paged pool: 139 MB
Non-paged pool: 57.9 MB

There is plenty of free memory on the host, to the point of being ridiculous (42.8 GB available...)

The memory buffer setting on the VM is set to 20%.

Is this expected behaviour? This condition has persisted for a few hours as we can see from our monitoring graph...

Please note that the memory graph shows megabytes of free memory.

Solution

Appears to be a known defect:

VMs may not get additional memory although they're set to use Dynamic Memory in Windows Server 2012 R2
https://support.microsoft.com/en-us/kb/3095308

Comments

[Per von Zweigbergk]

I had made an error in the question, there is no 2012 R2 anywhere, it's all 2012.

[Per von Zweigbergk]

This seems worth trying. I'm going to book a service window for Thursday and get this hotfix in. If the hotfix resolves the issue, I will award the bounty.

[Per von Zweigbergk]

I'm sorry, when I came to download the hotfix, I noticed that I made an error in asking the question. The question, originally, stated that the host was running Windows Server 2012 R2. Unfortunately, it turns out that it's actually running just Windows Server 2012. As such, the hotfix was not applicable in this scenario...

[Greg Askew]

Sometimes Microsoft back-ports hotfixes, but I wouldn't have much hope for it given that 2012 R1 has such a low market share and it is not security-related. You could always call and ask if they intend to make it available for R1 or if it is available as a private hotfix.