Large memory issues on 4-STABLE

Irvine Short irvine at
Sun Sep 14 22:07:46 PDT 2003

On Sun, 14 Sep 2003, Alex de Kruijff wrote:

> On Sat, Sep 13, 2003 at 03:48:21AM -0700, David G. Lawrence wrote:
> > > David Lawrence said:
> > > >   Sorry, due to design issues, it isn't possible to have virtual sizes
> > > >larger than about 3GB on FreeBSD. This is because the kernel is mapped in
> > >
> > > OK, fair enough. Is this going to be any different in FreeBSD with PAE
> > > (Intel's scheme for 32bit stuff using > 4GB RAM)?
> >
> >    No, this has nothing to do with the size of physical memory. It is a limit
> > on the size of a process's virtual address space.
> >
> > > Should I try 5.1? Or isn't 4.9 going to have PAE support anyway?
> >
> >    All versions of FreeBSD have this limitation.

Yes, I understand that. What I am saying is, is that the general story out
there is that with a 32 bit operatng system no process can address more
than 4GB of RAM. Fine. David said that in FreeBSD I cannot in practicality
address more than about 3GB of RAM. Also fine.

However we have a situation where if I set MAXDSIZ to 2048 or above then
things break, so FreeBSD right now has an effectivce limit of 2GB per

Is this to be considered a bug or a feature?

Then, with the PAE support, lets say I have 8GB of RAM. Will those same
design limitations restrict me to 3GB of RAM, or 2GB, or will I be able to
have a single process addressing 4GB all by itself?

This is relevant to the work we're doing - some of my users actually
really do need this amount of memory.



> >
> > > Given what David says though, why do I have a problem with MySQL getting
> > > thread errors with MAXDSIZ 2048 or greater?
> > >
> > > Why does tcsh's "limit" report datasize unlimited when MAXDSIZ is over
> > > 2048?
> >
> >    Probably a signed arithmetic problem. 2048MB is 2^31 bits, which is the
> > largest number that can be represented in a 32 bit signed int.
> Sorry but 2^31 is the lowest number availible in a 32 bit signed int and
> 2^31-1 is the largest number. The 32th bit indicates the number is
> negitive.

Irvine Short

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