Let’s say you decide to give each thread a 1 terabyte stack, on the off chance it will run a recursive algorithm where (stack frame size × iteration depth) appr

Let’s say you decide to give each thread a 1 terabyte stack, on the off chance it will run a recursive algorithm where (stack frame size × iteration depth) approximates that. (Ignoring memory usage for administration, that is doable on 64-bit systems. 1 terabyte is 2⁴⁰ bytes, so you could have 2²⁴ ≈ 16 million such stacks in a 64-bit virtual address space) Setting up the MMU to know about that will take time and memory, though. It also likely (details vary between systems) will introduce another layer of indirection in the tables used to translate virtual to physical addresses (https://en.wikipedia.org/wiki/Page_table https://en.wikipedia.org/wiki/Page_table) and thus slow them down. Workaround would be to use huge page sizes, but that at is wasteful because that not only means large page sizes in virtual memory, which is plentiful, but also in physical memory, which is much scarcer (even if the hardware would support 64 address lines and had 2⁶⁴ bytes of RAM, that still would be shared between processes)