x86 64bit system, grub2, ubuntu 14.04 LTS
linux kernel 4.5
/etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="cma64M@1G"
dmesg
[ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.5.0 root=UUID=caa92695-2d64-4af5-9c7e-d22c605d1f1e ro cma=1G@3G
[ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.5.0 root=UUID=caa92695-2d64-4af5-9c7e-d22c605d1f1e ro cma=1G@3G
[ 0.000000] Memory: 3919508K/4086104K available (7997K kernel code, 1278K rwdata, 3920K rodata, 1472K init, 1292K bss, 166596K reserved, 0K cma-reserved)