How should the crashkernel parameter be configured for using kdump on Red Hat Enterprise Linux 8 ?

Issue

• When configuring the crashkernel parameter the kdump service fails to start:

# systemctl start kdump
Job for kdump.service failed because the control process exited with error code.
See "systemctl status kdump.service" and "journalctl -xe" for details.
# systemctl status kdump
● kdump.service - Crash recovery kernel arming
   Loaded: loaded (/usr/lib/systemd/system/kdump.service; disabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Fri 2018-11-16 09:07:04 CET; 10s ago
  Process: 1164 ExecStart=/usr/bin/kdumpctl start (code=exited, status=1/FAILURE)
 Main PID: 1164 (code=exited, status=1/FAILURE)

11月 16 09:07:03 rhel8a.example.net systemd[1]: Starting Crash recovery kernel arming...
11月 16 09:07:04 rhel8a.example.net kdumpctl[1164]: Could not find a free area of memory of 0x1edb000 bytes...
11月 16 09:07:04 rhel8a.example.net kdumpctl[1164]: locate_hole failed
11月 16 09:07:04 rhel8a.example.net kdumpctl[1164]: kexec: failed to load kdump kernel
11月 16 09:07:04 rhel8a.example.net kdumpctl[1164]: Starting kdump: [FAILED]
11月 16 09:07:04 rhel8a.example.net systemd[1]: kdump.service: Main process exited, code=exited, status=1/FAILURE
11月 16 09:07:04 rhel8a.example.net systemd[1]: kdump.service: Failed with result 'exit-code'.
11月 16 09:07:04 rhel8a.example.net systemd[1]: Failed to start Crash recovery kernel arming.
# 

• What is the correct crashkernel parameter for kdump to work?
• "crashkernel reservation failed - memory is in use" errors when kernel panics