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[Jason Couture <plaguethenet@xxxxxxxxx>]

This bug is causing some serious issues for us with the 16.04 rollout.
We oversubscribe which is admittedly our problem, and our 16.04 VM's
spike to 8gb during boot, but then settle at a reasonable 2gb, but the
VM continues to hog 8gb to itself. We have 5 total, so that's a grand
total of 30GB that's held for no reason at all.

We get a single set of messages from the balloon driver at boot, and then nothing at all.
This is all we get:
[   62.565094] hv_balloon: Received INFO_TYPE_MAX_PAGE_CNT
[   62.565153] hv_balloon: Data Size is 8

uname -a:
Linux ContainerHost1 4.4.0-24-generic #43-Ubuntu SMP Wed Jun 8 19:27:37 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

/proc/version_signature:
Ubuntu 4.4.0-24.43-generic 4.4.10

free -h:
              total        used        free      shared  buff/cache   available
Mem:           7.9G        2.3G        4.8G        9.9M        830M        5.5G
Swap:          2.0G        721M        1.3G


Hyper V shows 7790MB assigned to this VM.
Hyper-V settings are set for 512-8192MB, with a 20% buffer.

According to Hyper-V's description of dynamic memory, this VM should
only have 2.76GB of ram attached to it at this point in time.

Hyper-V host is 2012 R2

Do we have any confirmation that this is actually a bug? Or any ETA on a
fix?

Can I help you collect more info to fix the problem?

-- 
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https://bugs.launchpad.net/bugs/1584597

Title:
  Hyper-V Memory Ballooning re-broken in 16.04

Status in linux package in Ubuntu:
  Triaged
Status in linux source package in Xenial:
  Triaged

Bug description:
  Regression: #1294283 fixed memory ballooning in Hyper-V in 14.04, but
  the bug has returned in 16.04.

  
  Steps to reproduce:

  1. Create Gen2 Hyper-V VM
  2. Install Ubuntu 16.04
  3. modprobe hv_balloon
  Memory usage according to Hyper-V Manager will not change

  
  This has been reproduced on 2 fresh Ubuntu Server 16.04 instances.

  I installed linux-generic-xenial on a 14.04 instance, rebooted,
  modprobe'd hv_balloon and memory usage in Hyper-V Manager reduced to
  the correct level.

  Environment:
  Host: Windows NanoServer 2016

  Ubuntu Server 16.04 version_signature: `Ubuntu 4.4.0-21.37-generic 4.4.6`
  Ubuntu Server 14.04 version_signature: `Ubuntu 4.4.0-22.40~14.04.1-generic 4.4.8`

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