Now that the library allows much larger data, it can kill
machines with less memory.

Fixes #28321

Change-Id: I98e1a5fdf812fd75adfb22bf01542423de405fe2
Reviewed-on: https://go-review.googlesource.com/c/143817Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>