I seem to experience a kernel crash (or application crash in early
moments of this bug) due to Hyper-V ballooning (or at least dynamic
memory). I am using Xenial on Hyper-V on Windows Server 2012 64bit. I
started using dynamic memory (1024 Kb start memory, allowed growing to
3072 Kb). Apparently this worked fine; I saw memory rise during demand
and memory was released back to the host when not needed. But the
releasing of memory apparently causes memory corruption. I noticed this
my using the stress tool that was called like this:

bme@zabbix:~$ stress --vm-bytes $(awk '/MemFree/{printf "%d\n", $2 * 0.9;}' < 
/proc/meminfo)k --vm-keep -m 1
stress: info: [3698] dispatching hogs: 0 cpu, 0 io, 1 vm, 0 hdd
stress: FAIL: [3699] (522) memory corruption at: 0x7fd801e00010
stress: FAIL: [3698] (394) <-- worker 3699 returned error 1
stress: WARN: [3698] (396) now reaping child worker processes
stress: FAIL: [3698] (451) failed run completed in 0s

The memory corruption only occured when Hyper-V had reclaimed memory
(balloning). Disabling dynamic memory has removed the memory
corruptions.

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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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