how to specify kernel parameter "memmap="

[Long Wind <longwind2009@gmail.com>]

I can't boot many Linux, probably because linux can't correctly detect
memory map
so I have to specify myself, below is copied from kernel-parameters.txt


memmap=exactmap	[KNL,X86] Enable setting of an exact
			E820 memory map, as specified by the user.
			Such memmap=exactmap lines can be constructed based on
			BIOS output or other requirements. See the memmap=nn@ss
			option description.


Could you help me specify "exactmap"?
I can't find details about it.
Thanks in advance!

(I go to bed now)