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

[Benoit St-Jean via Pharo-dev]

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Eliot,

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.n...@gmail.com <mailto:nicolas.cellier.aka.n...@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@lists.pharo.org <mailto:pharo-dev@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

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        Benoît St-Jean
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        "A standpoint is an intellectual horizon of radius zero".  (A.
        Einstein)




--
_,,,^..^,,,_
best, Eliot

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

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