Function _vm_domain_allocate

freebsd/vm/vm_page.c:2023–2056

* Returns true if the number of free pages exceeds the minimum * for the request class and false otherwise. */

 * for the request class and false otherwise.
 */
static int
_vm_domain_allocate(struct vm_domain *vmd, int req_class, int npages)
{
	u_int limit, old, new;

	if (req_class == VM_ALLOC_INTERRUPT)
		limit = 0;
	else if (req_class == VM_ALLOC_SYSTEM)
		limit = vmd->vmd_interrupt_free_min;
	else
		limit = vmd->vmd_free_reserved;

	/*
	 * Attempt to reserve the pages.  Fail if we're below the limit.
	 */
	limit += npages;
	old = vmd->vmd_free_count;
	do {
		if (old < limit)
			return (0);
		new = old - npages;
	} while (atomic_fcmpset_int(&vmd->vmd_free_count, &old, new) == 0);

	/* Wake the page daemon if we've crossed the threshold. */
	if (vm_paging_needed(vmd, new) && !vm_paging_needed(vmd, old))
		pagedaemon_wakeup(vmd->vmd_domain);

	/* Only update bitsets on transitions. */
	if ((old >= vmd->vmd_free_min && new < vmd->vmd_free_min) ||
	    (old >= vmd->vmd_free_severe && new < vmd->vmd_free_severe))
		vm_domain_set(vmd);

	return (1);
}

int
vm_domain_allocate(struct vm_domain *vmd, int req, int npages)