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List:       freebsd-amd64
Subject:    Re: memory allocation question
From:       "Steven G. Kargl" <kargl () troutmask ! apl ! washington ! edu>
Date:       2004-03-24 4:04:24
Message-ID: 200403240404.i2O44OOq033215 () troutmask ! apl ! washington ! edu
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Peter Wemm wrote:
> On Tuesday 23 March 2004 07:25 pm, Steven G. Kargl wrote:
> > I may have finally talked my boss into updating my computational
> > workstation (which runs FreeBSD).  The directions of our computations
> > is leading towards massive memory requirement.  So, the question is:
> > If I have an AMD64 system with 16GB of memory and appropriate kernel
> > options, can a single process allocate >15 GB for its use?
> 
> The default malloc limit is 8GB.  I picked that arbitarily because it 
> was double 4GB.  It is a tunable that can be changed at boot time.
> 
> However.. mmap() is unlimited.  You can use most of the remaining 128TB 
> of virtual memory for mmap.  You could also increase the malloc limit 
> to nearly 128TB if you wanted to.
> 
> The MAXDSIZ value is where malloc is limited.  It defaults to:
> #define  MAXDSIZ  (8192UL*1024*1024)
> It can be changed at kernel compile time with 'options MAXDSIZ' or 
> simply overridden at boot time by setting the tunable kern.maxdsiz.
> 

Thanks, Peter.  I knew about MAXDSIZ, but I didn't know if there
was some hard limit.  I can live with 128TB of virtual memory.
I thinking we can start with 16 GB of physical memory in a single
node and add nodes to cluster as our memory requirements increase.

-- 
Steve
http://troutmask.apl.washington.edu/~kargl/
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