rem: key.ref = cache_ref;
add: key.cache = cache_ref->cache;
context: vm_cache_lookup_page(vm_cache_ref *cache_ref, off_t offset){	vm_page *page;	int state;	struct page_lookup_key key;	key.offset = offset;	key.ref = cache_ref;	state = disable_interrupts();	acquire_spinlock(&page_cache_table_lock);	page = hash_lookup(page_cache_table, &key);	release_spinlock(&page_cache_table_lock);	restore_interrupts(state);	return page;}