bug#35067: 26.1; Editing particular .html file is slow.

[Eli Zaretskii]

On April 1, 2019 8:59:07 AM GMT+03:00, Scott Haines 
<scotthaines.mn@comcast.net> wrote:
> 
> 
> Dear Emacs maintainers:
> 
> Here are the steps to see Emacs editing this .html file very slowly.
> 
> 1. Copy the file
> http://gnuplot.sourceforge.net/demo_canvas_5.2/simple.html
> to your computer and open it in Emacs. 
> 
> 2. Press the down arrow key repeatedly.
> 3. Around row 55 Emacs will become very slow in its response.
> This .html file has JavaScript. This may or may not be significant.


That file has a 100K line in the area where you see slowdown.  Emacs has known 
problems with displaying very long lines.

On my system, the slowdown is bearable, at least in "emacs -Q", and turning on 
truncate-lines makes display fast again.  If you see this in a customized 
session, perhaps some of the customizations add more slowdown.