Re: Indentation and gc

[Eli Zaretskii <eliz@gnu.org>]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: spacibba@aol.com, arne_bab@web.de, emacs-devel@gnu.org
> Date: Mon, 13 Mar 2023 12:45:34 +0000
> 
> >                   If you specify a larger value, garbage collection will
> >      happen less often.  This reduces the amount of time spent garbage
> >      collecting, but increases total memory use.  You may want to do
> >      this when running a program that creates lots of Lisp data.
> >      However, we recommend against increasing the threshold for
> >      prolonged periods of time, and advise that you never set it higher
> >      than needed for the program to run in reasonable time.  Using
> >      thresholds higher than necessary could potentially cause
> >      system-wide memory pressure, and should therefore be avoided.
> 
> Unfortunately, if is not very clear how much increasing the threshold
> affects memory usage. What if I increase the threshold twice? Is it
> safe? Dangerous? Maybe 10%? 10x?

How should I know?  Does anyone know?

> I guess we can give an answer if we collect usage statistics.

Exactly.

> > Again, you are reasoning about the value as if it were related to the
> > maximum memory footprint Emacs could have.  But in fact, it is related
> > only to the _increment_ of memory Emacs can have before it should stop
> > and consider how much of that is garbage.
> 
> But how else should I interpret "memory pressure"?

Increasing the threshold indeed increases the danger of memory
pressure, but how exactly is yet unknown.  So simplistic
interpretations like this are IMO premature.

> But then there is a warning about memory
> pressure, but it does not look too scary if you have plenty of RAM,
> especially looking at common advises to increase the threshold across
> internet.

Using most-positive-fixnum as the threshold _should_ scare people.