bug#29889: 27.0.50; Slow visual selection

[Eli Zaretskii]

> From: Sujith <m.sujith@gmail.com>
> Cc: 29889@debbugs.gnu.org
> Date: Sun, 31 Dec 2017 14:12:23 +0530
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> > Since mark_object appears high in the profile, could you please
> > rerun the experiment after setting gc-cons-threshold and
> > gc-cons-percentage so as to avoid GC for the time of the expdriment?
> 
> After doing (setq gc-cons-threshold 1000000000), the issue doesn't
> seem to happen. The cursor moved around freely except for one
> interruption - maybe the GC kicked in then.

Oh, you are right: if I set garbage-collection-messages non-nil, I see
a GC message each time I move the cursor.

So I guess my original theory was probably wrong, and the actual
suspect is some code, yet to be discovered, that conses such large
amounts of Lisp data.  I will look into it if no one beats me to it.

Thanks!