Well, you can open /proc/$pid/maps and read it, but that is inefficient and
hackish. I don't know of a nice way to determine the total number of open mmaps
in a process.

One possible approach we'd discussed is indeed to maintain a LRU list of open
mappings and close the oldest one when a certain threshold number is reached.
This might be the easiest way to avoid the crashes, but some applications might
be hurt in terms of performance, if they expect to be able to update those
small buffers often.