Public bug reported:

Using linux-next 4.3.0-next-20151106 kdump is failing to start as a service.
On RHEL and SLES with upstream, kdump is working as expected so only Ubuntu has 
this issue as observed from our testing.

A similar issue with the same error message from kdump has been already 
reported here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1400319
However that behavior was on 32bit Ubuntu only, and now with upstream this 
seems to extend to 64bit as well.
So I'm not sure if we should link these 2 bug reports at this point.

Issues description:
1. kdump-tools service fails to start on 15.04 64bit, when runnig the 
linux-next kernel
Error returned is: Starting kdump-tools: Could not find a free area of memory 
of 0xa637000 bytes...
(full log below)
By default, kdump sets crashkernel to 394M-:128M

2. If crashkernel is set to 384M, the dump file will fail to create due to OOM 
messages when a crash is triggered. 
Attaching the full serial log with crashkernel=384M. The log is the same with 
512M as crashkernel.
Can this be a memory leak in the kdump kernel, making even already high values 
as 512M for the crashkernel to not be enough?
VM RAM has been set to 2GB and also 4GB, and with minimal load on the system 
that isn't a problem.

Work-around for issue #1:
Set crashkernel size to 384M, instead of the default 384M-:128M.
With this, kdump-tools will start.
However the dump file doesn't get written and the system will hang, without 
rebooting.

Values used to trigger a kdump:
- 384M
- 512M
- 384M-:128M - kdump-tools will not properly load.

Full kdump service log:
root@ubuntu1504srv:~# service kdump-tools status
รข kdump-tools.service - Kernel crash dump capture service
   Loaded: loaded (/lib/systemd/system/kdump-tools.service; enabled; vendor 
preset: enabled)
   Active: active (exited) since Wed 2015-11-11 06:02:28 PST; 20min ago
  Process: 792 ExecStart=/etc/init.d/kdump-tools start (code=exited, 
status=0/SUCCESS)
 Main PID: 792 (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/kdump-tools.service

Nov 11 06:02:20 ubuntu1504srv systemd[1]: Starting Kernel crash dump capture 
service...
Nov 11 06:02:28 ubuntu1504srv kdump-tools[792]: Starting kdump-tools: Could not 
find a free area of memory of 0xa637000 bytes...
Nov 11 06:02:28 ubuntu1504srv kdump-tools[792]: locate_hole failed
Nov 11 06:02:28 ubuntu1504srv kdump-tools[792]: * failed to load kdump kernel
Nov 11 06:02:28 ubuntu1504srv systemd[1]: Started Kernel crash dump capture 
service.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: hyper-v kdump-tools

** Attachment added: "serial log for kdump with crashkernel=384M"
   
https://bugs.launchpad.net/bugs/1515301/+attachment/4516967/+files/kdump_15.04_linux-next

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https://bugs.launchpad.net/bugs/1515301

Title:
  [Hyper-V] issues with linux-next on 15.04 kdump functionality

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