ARM64 Kdump cannot allocate crashkernel

In ARM64 server and installed memory around 128G, ubuntu default /etc/default/grub.d/kdump-tools.cfg default configuration might cause kdump allocate memory failed. error message as below

[ 0.000000] cannot allocate crashkernel (size:0x80000000)
[ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.18.0-25-generic root=UUID=ee8be10d-d649-425d-a807-640751836186 ro console=tty0 crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M

reserve memory is for RAM disk. root cause might be system cannot allocate enough memory for crash kernel.

Reduce allocate memory size will work

dmesg | grep crash
[ 0.000000] crashkernel reserved: 0x00000000bfe00000 – 0x00000000ffe00000 (1024 MB)
[ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.18.0-25-generic root=UUID=ee8be10d-d649-425d-a807-640751836186 ro console=tty0 crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:1024M,high,128G-:16384M