Date: Sat, 11 Nov 2000 14:15:08 -0800 From: Doug Barton <DougB@FreeBSD.org> To: Mitch Collinsworth <mitch@ccmr.cornell.edu> Cc: freebsd-questions@FreeBSD.org, Mitch Collinsworth <mitch@mercury.ccmr.cornell.edu> Subject: Re: Linux malloc better on FreeBSD than FreeBSD malloc? Message-ID: <3A0DC4EC.509A982C@FreeBSD.org> References: <Pine.LNX.4.10.10011111153160.16421-100000@dragon.ccmr.cornell.edu>
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Mitch Collinsworth wrote:
>
> Well I hope that subject was provocative enough to generate some
> interest! :-) Here's a strange situation that's bugging me. I
> recently changed jobs, into a dept that's heavily Linux-based. I
> of course have different preferences, but need to demonstrate
> technical superiority if any changes are going to happen. An
> opportunity just arose to make some comparisons between Linux and
> FreeBSD in maximum process size. We have some new systems with
> 4 GB RAM each that will be made available for running large batch
> jobs.
>
> We have a very simple test program that malloc's successively larger
> and larger blocks of memory until it fails, freeing the current blocks
> after each successful trial. The strange thing is that the test
> program runs much farther on FreeBSD using the Linux binary in
> compatibility mode than it does using the binary compiled on FreeBSD!
> Included below are the output from each binary and the source. Can
> anyone explain these results?
>
> A second question, which is the primary issue we were trying to
> discover is if it is possible for a single process to malloc more than
> 2 GB of memory. FreeBSD supposedly supports up to 4 GB (on Intel
> hardware), but does anyone know if there is still a 2 GB per process
> limit? And if a single process can be larger than 2 GB, is there a
> 2 GB limit on any single malloc with that process?
You've left out several important details, namely what version of
freebsd you're using and what kind of, if any kernel tuning you've done.
If you haven't already, read through LINT/NOTES to learn about some of
the options available. In particulary I'm guessing you will need to take
advantage of MAXDSIZ and possibly DFLDSIZE. You may also want to play
around with some of the other VM options, but a lot of that stuff is
really poorly documented. If you can contribute hard data regarding
performance with any of those options (or combinations) enabled, I'm
sure it will be well appreciated.
Good luck,
Doug
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