There's a better solution than falling back to buffered io

At least for small pages, much of the cost of using the page cache is actually in setup, insertion, and removal from the cache, *not* in memory allocation or data copying. Depending on the use case and hardware, simple bounce buffers can be *much* faster. And they can be done in parallel across many threads without conflicting on the tree locking for the page cache. (Even a read is a tree insert unless the data is already present.)

But this becomes proportionally less true with large folios though, probably to the point of not really true for larger sizes, since the overhead is spread over much more data.