bug#24565: 25.1: info freezes on some elements

[Eli Zaretskii]

> From: Nikolay Kudryavtsev <nikolay.kudryavtsev@gmail.com>
> Cc: 24565@debbugs.gnu.org
> Date: Sat, 1 Oct 2016 11:55:44 +0300
> 
> That commit removed defines that effectively commented out 
> compact_font_cache_entry on Windows

Indeed, and on purpose.  That code was ifdef'ed away because it caused
serious problems on Windows that couldn't be resolved for the next
release.  Now they are mostly resolved, so having some code run on
most platforms, but not on Windows, is bad for maintainability.

In particular, not compacting the font cache can potentially bloat the
Emacs memory footprint to humongous proportions, although this only
happens in some rare scenarios.

> comment there links to #15876, which seems to be the original report
> for this bug.

AFAIR, we never got to the bottom of that bug, but perhaps it indeed
has the same reason.

I'm sorry, but none of the active developers here know enough about
font handling in Emacs to fix these issues in a more thorough way.  So
for the time being, if some specific rarely-used font causes
performance degradation, and no simple and safe fix could be found,
the only remedy is to refrain from using that particular font.