bug#16129: 24.3.50; Emacs slow with follow-mode when buffer ends before last window

[Eli Zaretskii]

> Date: Fri, 13 Dec 2013 15:34:07 +0100
> From: Anders Lindgren <andlind@gmail.com>
> 
> I am the original author of follow-mode, so I can share one interesting
> implementation detail. When the viewed buffer ends before the last window,
> follow-mode tries to display this window without any content (by setting
> the window start to point-max). Unfortunately, the Emacs display engine
> always tries ensure that windows are not empty so it repositions it...

You cannot have window-start and point-max, sorry.  Remember:
point-max is a buffer position that doesn't really exist, it's beyond
the end of buffer text.  So it cannot be treated as any other buffer
position.