Why is VmallocTotal 34359738367 kB?

/proc/meminfo has a memory statistic VmallocTotal. It is described as > Total size of vmalloc memory area. in [proc's man page](https://man7.org/linux/man-pages/man5/proc.5.html) and elsewhere as > Total memory available in kernel for vmalloc allocations It sparked my curiosity because it is a very high number and everywhere I searched it is exactly 34359738367 kB. It seems like an arbitrary maximum. But what is the significance of 34359738367 kB? It is not a multiple of 2, not a prime number, but it is 0x7FFFFFFFF in hexadecimal. I also noticed pmap process memory map addresses max out at 0x7FFFFFFFF. But then what is the practical significance of 0x7FFFFFFFF?