bug#44983: Truncate long lines of grep output

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: Dmitry Gutov <dgutov@yandex.ru>,  44983@debbugs.gnu.org
> Date: Tue, 01 Dec 2020 22:35:55 +0200
> 
> >> Perhaps (setq truncate-lines t) could help in that case?
> >
> > Not necessarily, because the truncated parts are still in the buffer,
> > and the display code which is slow in that case basically moves
> > through the buffer one character at a time in many cases.  Only some
> > specific scenarios (read: a small number of commands) can jump to the
> > next physical line disregarding the truncated parts.
> 
> It's very strange that after adding the text property 'display "[…]"
> on a very long line, motion commands are still very slow in that buffer.
> 
> Could you help to understand why hiding long regions
> doesn't help to improve performance?

I can try, but please tell which commands are slow.  Is it C-f/C-b,
C-n/C-p, C-v/M-v, something else?