/*
 * Find a stack vm_area (VM_GROWSDOWN) that includes <sp>.
 * A stack is LIFO so what is used is sp...vm->vm_end
 * The area vm->vm_start...sp is unused. Possibly free/unmap
 * part of the unused with respect to max_unused.
 * max_unused does not need to be page aligned:
 *	suppose unused stack 5000 bytes, max_unused = 900
 *	we free a page and have 1004 bytes of unused stack. Ok
 * -- sxanth@ceid.upatras.gr
 */
asmlinkage int sys_adjstack (unsigned long sp, unsigned long max_unused)
{
	struct vm_area_struct *vma;
	unsigned long d;

	if (!(vma = find_vma (current->mm, sp)) || !(vma->vm_flags & VM_GROWSDOWN))
		return -EINVAL;

	d = sp - vma->vm_start;

	if (d <= max_unused) return 0;

	d -= max_unused;
	d &= PAGE_MASK;		/* downwards alignment to page size */

	if (d) {
		int ret;

		down(&current->mm->mmap_sem);
#if LINUX_VERSION_CODE < 0x020300
		lock_kernel ();
		ret = do_munmap (vma->vm_start, d);
		unlock_kernel ();
#else
		ret = madvise_vma (vma, vma->vm_start, vma->vm_start + d, MADV_DONTNEED);
#endif
		up(&current->mm->mmap_sem);
		return ret;
	}

	return 0;
}