Re: Garbage collector: is 800kb a good default?

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: dim1212k@gmail.com,  emacs-devel@gnu.org
> Date: Thu, 09 Apr 2020 14:42:56 -0400
> 
> > Let's not forget that running GC while Emacs is idle will make Emacs
> > less responsive if the user starts typing while GC is in progress,
> 
> The argument for GC-when-idle goes that if this happens it's not really
> worse than what we have now, because if the GC hadn't started "before
> the user starts typing", it would have run as part of the command
> launched by the user, so from the user's point of view there's no
> noticeable difference.

The difference is that when an idle timer runs a long uninterruptible
calculation, the user thinks Emacs is idle, so having a character
appear, or Emacs respond to a command with a prompt, after a
significant delay makes a very bad UX.  By contrast, when a command is
running, the user will normally know that Emacs isn't idle, so a
delayed response will be less of a surprise.

> > Also, we already try running GC each time Emacs becomes idle.
> 
> Do we?  I thought so as well, but I couldn't see any evidence of it in
> the code.

It's in keyboard.c, right after we auto-save when enough idle time has
passed:

      /* If there is still no input available, ask for GC.  */
      if (!detect_input_pending_run_timers (0))
	maybe_gc ();