Why crashkernel=auto fails to reserve memory on certain hardwares?

Issue

• Why crashkernel=auto fails to reserve memory on certain hardwares?
• When configuring the crashkernel=auto parameter it shows the below messages.

Mar 13 11:14:42 host1 kernel: Using crashkernel=auto, the size chosen is a best effort estimation.
Mar 13 11:14:42 host1 kernel: Cannot reserve 256MB crashkernel low memory, please try smaller size.


# 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

Mar 13 09:31:04 host1: kdumpctl[2785]: kdump: No memory reserved for crash kernel
Mar 13 09:31:04 host1: kdumpctl[2785]: kdump: Starting kdump: [FAILED]
Mar 13 09:31:04 host1: kdump.service: Main process exited, code=exited, status=1/FAILURE
Mar 13 09:31:04 host1: kdump.service: Failed with result 'exit-code'.
Mar 13 09:31:04 host1: Failed to start Crash recovery kernel arming.