Only if they're resident. Otherwise you just need one page per thread of physical memory (so ~40MB on x86) and 10GB of virtual memory.

While that's strictly true, resident memory in this context is a function of worst case memory usage by the code executing on those stacks. Seems wise to assume worst case performance when discussing this.

The program could use one page's worth of stack space, which is optimal. The program could use like 200 bytes of stack space, which wastes the rest of the page. The program could recurse all the way to 9.9 MB of stack usage, stop just before overflow and then unwind back to constant 200 bytes stack space usage, and never touch all those pages ever again.