[Pharo-dev] Bug 18632 : Virtual Machine parameters need to be documented

Benoit St-Jean bstjean at yahoo.com
Fri Feb 7 21:34:30 EST 2020


I was referring to VM parameters (aka #vmParameterPut:at:).  But now 
that you mention it, it adds another level of complexity. When you 
specify something in the command line arguments, how do you resolve the 
fact that the command line argument tells you something that is 
different from what is in the image? The mechanics of the VM stuff is 
like black magic to most of us! You see, that's the type of question 
that is kinda "oral tradition" : if no one ever told you, you don't know 
since it's not obvious and rarely documented properly but, eh, it's 
written "somewhere" in the code of the VM! It might seem obvious to a 
very few of you, especially yourself, since you've been working on the 
VM long before my Vassili-Bykov-Days but for most of us, it's a case of 
very-interesting-to-read-but-way-too-complex ! ;)

To make a long story short, I was thinking about experimenting and 
trying to implement "stuff" with something similar to VisualWorks's 
MemoryPolicy (AbstractMemoryPolicy and subclasses to be more precise) 
for Pharo. It did save my/our/TheProjects' ass quite a few times. Yes, 
you can write scripts to customize a few things before you produce the 
"final" image but it is a pain in the as_ (the polite SQL way of 
describing it) and you have to keep track of artifacts (scripts, files, 
workspace code, whatever) to produce the final image.  With custom 
memory policies, everything resides in the image and it is sooooooooooo 
much simpler to deal with!

There is no such thing as a one-configuration-fits-all.  That's why 
different types of applications have different needs for GC, memory, 
tenuring, memory-space sizes, etc. And quite frankly, VW' MemoryPolicy 
is so far and by far the best solution I've seen to cope with that. 
There ain't such thing as 2 identical applications that have the exact 
same VM/GC/memory needs!

I was able to build/read a "collection" of articles/posts/PDFs about GC 
and the VM but, quite honestly, I kinda lost track of what is what and 
which is which.  Cog, Spur, stack or not, NewSpeak vs Squeak vs Pharo, 
32 vs 64 bits, jitted or not, and all permutations you can think of, for 
99.9% of us it is like trying to learn Mandarin in 2 days! I do/did read 
your blog as well as the blog of Clément Béra as well as Andres Valloud 
posts/papers on the subject but in the VM world, things quickly get 
complicated unless, like Obélix, you were born in it! I've read a 
gazillion papers on the GC and various Smalltalk memory models written 
by John McIntosh but are those papers/posts/articles still relevant?

In other words Eliot (and your VM wizard friends), the VM (aka GC and 
memory model) do need some "documentation love" for "the average 
Smalltalker" !  ;)

On 2020-02-07 13:59, Eliot Miranda wrote:
> Hi Benoit,
> On Fri, Feb 7, 2020 at 8:20 AM Nicolas Cellier 
> <nicolas.cellier.aka.nice at gmail.com 
> <mailto:nicolas.cellier.aka.nice at gmail.com>> wrote:
>     Hi Benoit,
>     for some reason (?), your email was marked as SPAM in gmail...
>     There is a short description in primitiveVMParameter, which is
>     found in generated code, for example:
>     https://raw.githubusercontent.com/OpenSmalltalk/opensmalltalk-vm/Cog/src/vm/gcc3x-cointerp.c
>     or VMMaker source code (you can also find VMMaker source code in
>     pharo vm github repo, no time to dig).
>     Le jeu. 6 févr. 2020 à 12:45, Benoit St-Jean via Pharo-dev
>     <pharo-dev at lists.pharo.org <mailto:pharo-dev at lists.pharo.org>> a
>     écrit :
>         I was looking for some documentation on VM parameters (are
>         they read,
>         read-write or write only as well as the expected argument
>         type) and came
>         across that issue on the old FogBugz database.
> Are you talking just about vmParameterAt:[put:]/vm parameterAt:[put:] 
> or are you also talking about command line arguments (pharos-vm 
> --help/squeak -help)?
> If the former, there are much more current comments in trunk Squeak 
> SmalltalkImage>>vmParameterAt:[put:] than in Pharo; you could usefully 
> copy that across. The comments in the two methods accurately specify 
> which parameters are read/write, and which persist in the image header.
> But I agree, more verbose documentation would be very helpful; the 
> current documentation is very terse, and while it describes what the 
> parameters are and whether they are writable, it really doesn't 
> describe what the systems that they operate on actually do.  I'm happy 
> to collaborate with you in developing better documentation.  If you 
> will do the writing I will happily consult.  Does that work?
>         https://pharo.fogbugz.com/f/cases/18632/Virtual-Machine-parameters-need-to-be-documented
>         I tried looking it up on GitHub but couldn't find it. Am I
>         missing
>         something or I should open an issue?  I'm working on something
>         related
>         to various memory settings and not having any info on a lot of
>         these
>         parameters doesn't help.  While I could meticulously read tons
>         of C code
>         of the VM and pinpoint exactly what I need to know for each
>         and everyone
>         of these undocumented parameters, I'd gladly do it myself if
>         any of the
>         VM guys (Clément, Pablo, Alexandre or Eliot) have
>         notes/documents/links
>         that could help me do it.
>         tia
>         -- 
>         -----------------
>         Benoît St-Jean
>         Yahoo! Messenger: bstjean
>         Twitter: @BenLeChialeux
>         Pinterest: benoitstjean
>         Instagram: Chef_Benito
>         IRC: lamneth
>         GitHub: bstjean
>         Blogue: endormitoire.wordpress.com
>         <http://endormitoire.wordpress.com>
>         "A standpoint is an intellectual horizon of radius zero".  (A.
>         Einstein)
> -- 
> _,,,^..^,,,_
> best, Eliot

Benoît St-Jean
Yahoo! Messenger: bstjean
Twitter: @BenLeChialeux
Pinterest: benoitstjean
Instagram: Chef_Benito
IRC: lamneth
GitHub: bstjean
Blogue: endormitoire.wordpress.com
"A standpoint is an intellectual horizon of radius zero".  (A. Einstein)

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