Apply suggestions from code review

Author: nagisa

src/lib.rs

@@ -154,7 +154,7 @@ psm_stack_manipulation! {
                 // `StackRestoreGuard` allocates a memory area with suitable size and alignment.
                 // It also sets up stack guards if supported on target.
                 let guard = StackRestoreGuard::new(requested_stack_size);
-                let (stack_base,allocated_stack_size) = guard.stack_area();
+                let (stack_base, allocated_stack_size) = guard.stack_area();
                 debug_assert!(allocated_stack_size >= requested_stack_size);
                 set_stack_limit(Some(stack_base as usize));
                 // TODO should we not pass `allocated_stack_size` here?

src/mmap_stack_restore_guard.rs

@@ -23,8 +23,6 @@ impl StackRestoreGuard {
             .checked_mul(page_size)
             .expect("unreasonably large stack requested");
 
-        // Next, there are a couple of approaches to how we allocate the new stack. If it is
-        // available, we take the most obvious path and use `mmap`.
         unsafe {
             let new_stack = libc::mmap(
                 std::ptr::null_mut(),
@@ -47,7 +45,7 @@ impl StackRestoreGuard {
                 old_stack_limit: get_stack_limit(),
             };
             // We leave a guard page without read/write access in our allocation.
-            // TODO we allocated two extra pages for guard pages, but here we only use one?
+            // There is one guard page below the stack and another above it.
             let above_guard_page = new_stack.add(page_size);
             #[cfg(not(target_os = "openbsd"))]
             let result = libc::mprotect(