Function kmapent_alloc

freebsd/vm/vm_map.c:188–220

* Allocate a new slab for kernel map entries. The kernel map may be locked or * unlocked, depending on whether the request is coming from the kernel map or a * submap. This function allocates a virtual address range directly from the * kernel map instead of the kmem_* layer to avoid recursion on the kernel map * lock and also to avoid triggering allocator recursion in the vmem boundary * ta

 * tag allocator.
 */
static void *
kmapent_alloc(uma_zone_t zone, vm_size_t bytes, int domain, uint8_t *pflag,
    int wait)
{
	vm_offset_t addr;
	int error, locked;

	*pflag = UMA_SLAB_PRIV;

	if (!(locked = vm_map_locked(kernel_map)))
		vm_map_lock(kernel_map);
	addr = vm_map_findspace(kernel_map, vm_map_min(kernel_map), bytes);
	if (addr + bytes < addr || addr + bytes > vm_map_max(kernel_map))
		panic("%s: kernel map is exhausted", __func__);
	error = vm_map_insert(kernel_map, NULL, 0, addr, addr + bytes,
	    VM_PROT_RW, VM_PROT_RW, MAP_NOFAULT);
	if (error != KERN_SUCCESS)
		panic("%s: vm_map_insert() failed: %d", __func__, error);
	if (!locked)
		vm_map_unlock(kernel_map);
	error = kmem_back_domain(domain, kernel_object, addr, bytes, M_NOWAIT |
	    M_USE_RESERVE | (wait & M_ZERO));
	if (error == KERN_SUCCESS) {
		return ((void *)addr);
	} else {
		if (!locked)
			vm_map_lock(kernel_map);
		vm_map_delete(kernel_map, addr, bytes);
		if (!locked)
			vm_map_unlock(kernel_map);
		return (NULL);
	}
}

static void
kmapent_free(void *item, vm_size_t size, uint8_t pflag)