Is that `wordcount` in Zig? My understanding (which could be wrong) is that reallocation in Zig would leave the old buffer "alive" (from the allocator's perspective) if it couldn't be expanded, meaning that you'd eventually OOM if a large enough contiguous region couldn't be found.
It's in zig but I just call mmap twice at startup to get one slab of memory for the whole file plus all the space I'll need. I am not sure whether Zig's GeneralPurposeAllocator or PageAllocator currently use mremap or not, but I do know that when realloc is not implemented by a particular allocator, the Allocator interface provides it as alloc + memcpy + free. So I think I would not OOM. In safe builds when using GeneralPurposeAllocator, it might be possible to exhaust the address space by repeatedly allocating and freeing memory, but I wouldn't expect to run into this on accident.
