Moving around point (using the cursor keys) in Xah’s unicode.txt in fundamental-mode is noticeably slower than in an ordinary text file. Are the many non-ASCII characters the issue? Anything else?

About: GNU Emacs 25.2.1 (x86_64-w64-mingw32) of 2017-04-24 started with option -Q

  • I can see all characters and I do not have slow downs, neither in text-mode nor fundamental-mode. I'm using 24.5 GTK with Linux. How are you moving point, by keyboard input?
    – jue
    Jun 13 '17 at 12:50
  • 3
    github.com/purcell/emacs.d/issues/273 see if this is relevant.
    – wvxvw
    Jun 13 '17 at 12:57
  • I see no problem on OSX either using Emacs 25.2.1.
    – lawlist
    Jun 13 '17 at 16:09

Reading the GitHub discussion thread linked in @wvxvw’s comment, I discovered the variable inhibit-compacting-font-caches. Setting it to non-nil solves the issue:

(setq inhibit-compacting-font-caches t)

Now navigating point is fast. According to the variable’s documentation, inhibiting compacting font caches comes at the expense of more memory usage, which is fine for me.

See also bug 27350 filed by @Drew.

  • You can accept your own answer (or any other answer, if you want to wait for others).
    – Drew
    Jun 13 '17 at 14:24
  • 1
    I just filed an enhancement request (bug #27350) to make the variable customizable.
    – Drew
    Jun 13 '17 at 14:35
  • 1
    I also filed bug #30539, which is similar - involves slowness due to the same variable.
    – Drew
    Feb 23 '18 at 2:48
  • Thanks that really works for me too. Oct 29 '18 at 18:33
  • Still works for Emacs 26 Win 64
    – Carsten H
    Nov 4 '19 at 9:19

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