points out that 404 responses are cached indefinitely.
When using the database cache backend, or another backend that does not limit storage space via LRU or similar, this can lead to cache filling in the case of either a large number of real 404s or a mis-behaving crawler.
Set a shorter TTL for 404 responses in page_cache module, so that they get expired after time rather than only via cache tags.
Consider whether to do this for all cache backends, or only those that don't support LRU or other space limitation - this would require a way for cache backends to indicate whether they do this though, which we don't have yet.
User interface changes
Data model changes