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Re: Loading tramp for dump goes into infinite regress

From: Eli Zaretskii
Subject: Re: Loading tramp for dump goes into infinite regress
Date: Mon, 25 Jul 2022 16:56:06 +0300

> From: Lynn Winebarger <owinebar@gmail.com>
> Date: Mon, 25 Jul 2022 08:49:27 -0400
> Cc: michael.albinus@gmx.de, emacs-devel <emacs-devel@gnu.org>
> > > it seems like something undesirable is going on between dumping and
> > > the native compilation unit.
> >
> > I find this hard to believe.
> If I can recreate it in a more direct way on my personal machines, I'll put 
> in a bug with details including the
> required modifications to tramp.el (to remove the problematic require of 
> tramp-loaddefs).

Please do.

> > Btw, you are aware that dumping *.eln files basically dumps just their
> > names, not their code?  And that, when you start Emacs after dumping,
> > it will load all of those *.eln files one by one, which takes time
> > (*.eln files are just shared libraries, like *.so files), and use up
> > shared-library and handle slots of the Emacs process?  So I'm not even
> > sure doing this would make sense from the performance POV: it could be
> > that startup will slower, not faster.
> I am aware that dumping the eln files produces an indirection to the shared 
> library, but not the details of the
> implementation.
> I would expect (or at least hope) that the effect of the evaluation that is 
> done on loading to be stored in the
> dump and for the shared libraries to get loaded into the process without 
> repeating the evaluation.  So things
> like the order of customization groups should be fixed.

It depends on the top-level forms of the package, and what they do.
If they change values of variables, those values will be dumped, yes.

> I would also expect that whatever the effect is on the emacs process with 
> .eln files loaded by the dumped
> file, it is no worse than it would be if loaded as part of my .emacs file.

How is this different from the previous expectation of yours?

> Another benefit I expect from native-compilation, dumped or not, is more 
> efficient memory use when running
> multiple emacs processes.  With dumping, I would expect (or hope for) better 
> garbage collector behavior
> since the amount of allocation required for the loaded modules should be 
> pre-determined (whether byte- or
> native-compiled).  If the image is 300MB (including the shared libraries), so 
> be it, as long as the memory is
> shared between multiple processes.  

I don't think I understand this expectation, and I don't think
natively-compiled code has any advantages wrt GC over the
byte-compiled code.

> I'd also like a baseline expectation of performance with native-compiled 
> libraries in the dumped image.

What kind of performance?

> > In any case, I'd suggest to get this working with *.elc files in a
> > build without native compilation support, before you try it with
> > native compilation.
> First I'll see if I can get the ordering straightened out with just the core 
> emacs files required by these
> packages, then do a test between byte-compiled and native-compiled on those.

I'm saying that your job could be easier if you did the first step
with byte-compiled files.

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