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The more you load Emacs up with packages, the more it starts to chug. Throw on a theme and an lsp client, and you might start to notice frequent stuttering.

This problem was very frustrating for me - I want to be able to hold C-n and linearly move down the document, micro-stutter free. I spent weeks searching for the problem, and considered quitting Emacs altogether.

Garbage Collection

It turns out that the problem wasn't that packages were executing slowly, it was the garbage that they were building up.

Emacs' garbage collector waits until a byte threshold (the gc-cons-threshold variable) has been reached before executing. Its default value feels relatively low for a modern computer - only 800KB. This results in frequent garbage collections, each causing a small stutter. Luckily, as with most things in Emacs, you can tune this behaviour.

If you want to see how frequently the GC is triggered, try setting garbage-collection-messages to non nil (you might be surprised).

Opinions on the ideal solution differ.

• Some people recommend increasing the threshold, leading to longer times without triggering the GC but longer stutters.
• Others recommend lowering the threshold, causing more frequent GC triggers but smaller stutters.
• The minibuffer (especially with packages like vertico) can use a lot of memory, so some recommend increasing the threshold only when using it.

The Solution

In my opinion, the best solution is to garbage collect when idle. When editing, you're often pausing briefly - and if there is little garbage, Emacs can collect it very quickly. I also basically disable the threshold entirely when in the minibuffer. Here's the code from my init.el.

(defun my-minibuffer-setup-hook ()
  (setq gc-cons-threshold most-positive-fixnum))

(defun my-minibuffer-exit-hook ()
  (setq gc-cons-threshold 800000000))

(setq gc-cons-threshold most-positive-fixnum)

(run-with-idle-timer 1.2 t 'garbage-collect)

I have been using this for a few months and it's worked perfectly. I've tried my best to notice the garbage collections, I haven't been able to.

There is a package for this, called the Garbage Collector Magic Hack. Personally I prefer a lower idle time than its default, and I like keeping it in my own config.