> you will use 10GB to do nothing.

You don't pay for stack space you don't use unless you disable overcommit. And if you disable overcommit on modern linux the machine will very quickly stop functioning.

▲ simonask 3 hours ago | parent [-]

The amount of stack you pay for on a thread is proportional to the maximum depth that the stack ever reached on the thread. Operating systems can grow the amount of real memory allocated to a thread, but never shrink it.

It’s a programming model that has some really risky drawbacks.

	▲	matheusmoreira 2 hours ago \| parent [-]
		> Operating systems can grow the amount of real memory allocated to a thread, but never shrink it. Operating systems can shrink the memory usage of a stack. `madvise(page, size, MADV_DONTNEED);` Leaves the memory mapping intact but the kernel frees underlying resources. Subsequent accesses get either new zero pages or the original file's pages. Linux also supports mremap, which is essentially a kernel version of realloc. Supports growing and shrinking memory mappings. `stack = mremap(stack, old_size, old_size / 2, MREMAP_MAYMOVE, 0);` Whether existing systems make use of this is another matter entirely. My language uses mremap for growth and shrinkage of stacks. C programs can't do it because pointers to stack allocated objects may exist.