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