bug#56682: locked narrowing

[Eli Zaretskii]

> Date: Tue, 29 Nov 2022 21:29:59 +0200
> Cc: 56682@debbugs.gnu.org, gregory@heytings.org, monnier@iro.umontreal.ca
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> >> That's the regression.
> > The faster ones use a different major-mode, btw.
> 
> The old (faster) revision uses js-mode, the new one -- the optimized 
> js-json-mode. I'm sure I could have made a mistake doing that 
> optimization, but the behavior doesn't indicate that: the delays are 
> higher near BOB and seem absent near EOB (in master/emacs-29), and they 
> don't show up in the profiler in separate leaf nodes (the previous ones 
> -- which I worked on optimizing -- did).

I didn't say the new mode was the culprit (you could have assumed I tried
the old mode as soon as I discovered this change since July).  I just
mentioned this for completeness, so we are aware what we are comparing.

Anyway, do you see any effect if you set long-line-threshold to nil?  Here
it makes the redisplay after insertion instantaneous (and this is an
unoptimized build, where without setting that variable to nil each insertion
in dictionary-pp.json takes about half a second).