The maximum available 134215624K is almost exactly 128 GiB:
(134215624 + 2104 ) / 1024.0 / 1024.0
The correction factor of 2104 comes probably from further hardware reservations and memory mappings. The lower value was a start value and there are further "freeing" messages logged in my dmesg so that this number increased eventually to:
The Linux kernel reserves some memory to administer the available memory. This administration takes a few percent of the memory and when you have hundreds of GB's of memory, that means that a few GB is not available.
Also, some memory is reserved per CPU and with more cores today, it also becomes noticeable. I have 16 cores but my BIOS says that 32 is possible, so I can get a little memory back with this possible_cpus=16 kernel parameter.
All in all, there is not much you can do: it takes memory to manage memory.