rem: return 0;
add: return B_OK;
context: vm_cache_insert_region(vm_cache_ref *cache_ref, vm_region *region){	mutex_lock(&cache_ref->lock);	region->cache_next = cache_ref->region_list;	if (region->cache_next)		region->cache_next->cache_prev = region;	region->cache_prev = NULL;	cache_ref->region_list = region;	mutex_unlock(&cache_ref->lock);	return 0;}