The explanation of page_size is extremely limited.
Example from the logging API:
maximum number of entries to return, If not passed, defaults to a value set by the API.

If you're familiar with gRPC then this makes sense, but for newcomers this is extremely limited information. Simple wording change can make a lot of difference here IMHO. Looking at this example from the Cloud Spanner Javadocs shows a slight change, but makes it easier to understand:
Specifying this will cause the list operations to fetch at most this many records in a page.

On a semi-related note, having usage examples would also clarify the usage a lot, but this can be said for all methods in the whole python library.