bug#57207: 29.0.50; Fontification is slow after e7b5912b23 (Improvements to long lines handling)

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@gmail.com>
> Cc: Gregory Heytings <gregory@heytings.org>,  57207@debbugs.gnu.org
> Date: Mon, 15 Aug 2022 19:41:23 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > If they do, can you put a breakpoint in xdisp.c here:
> > ...
> >
> > and see how frequently this gets called in the same buffer when you do
> > whatever shows the performance degradation?
> 
> Could you please clarify what exactly do I need to look for? What do you
> mean by frequency? Should I share some kind of gdb log?

I will, if your information from the "hung" Emacs will not give us a
good clue.  Given what you say there, it sounds like my theory behind
the above doesn't hold water, because it cannot explain the effect of
enlarging long-line-threshold that you experience.