[Bug 241710] please increase ARG_MAX

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=241710

--- Comment #12 from Pedro F. Giffuni <pfg at FreeBSD.org> ---
(In reply to Konstantin Belousov from comment #11)
> (In reply to Pedro F. Giffuni from comment #10)
> 2048 is a strange multiplicator.

I can write it 2 * 1024. I looked around and I noticed the value was a multiple
of 1024 on most platforms. It is admitedly an arbitrarily a number between what
we have and what Illumos uses for 32 bit archs. Having uncertain multipliers is
better than uncertain numbers.

> But you still ignore the crucial question: does increase cause issues for KVA
> starved arches.  If it is not, then introducing such gratuitous difference is 
> pointless.  If it is, might be we should bump the size for LP64 much more 
> aggressive.

I am indeed ignoring the question :(. I admitedly don't know what I am doing
here (note that I haven't grabbed the PR), I am just doing an educated guess in
the hopes that someone else comes with a real solution.

I understand it would be better to have a unique value for all platforms, I
just don't have a KVA-starved platform to test it or sufficient understanding
on the kernel to determine it (I am looking at exec_alloc_args_kva() and I see
a linked list, beyond that the numbers escape me).  OTOH, I see historic
evidence that we don't want to jump such values arbitrarily.

If we are severely KVA limited on non _LP64 platforms, then it makes perfect
sense to avoid the bump on those platforms (I doubt we want to run Code Aster
on a Raspberry Pi anyways), and Illumos discriminates archs already although
with much higher values. I personally don't see a reason to bump ARG_MAX more
than absolutely necessary: I just want software to compile and wasting more
precious KVA memory doesn't serve any purpose. If we have to revise the value
every ten years, so be it: people can always check the ARG_MAX value with
getconf and report it.

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