The oh-so-smart idea from 39c2568e was
pretty dumb after all:

While testing with the low RAM config (16MB on 10GB), a lockop was found
with only ~45% of RAM occupied. The reason for the lockup was the
un-crammed 64KB (16bits) request for a regionlist with priority 4, which
was blocking all other requests.

So: No, trying to allocate something "just in case" is never a good
idea.