[Leaplist] LINUX memory shortfall

[Kyle Gonzales]

The split is 3gb/1gb on a normal 32-bit kernel.  3 Gb is for user
space and 1 Gb is for kernel space.  If you use the SMP kernel in
older distros, and the regular kernel (which is combined uniproc &
SMP) that limit is 16 Gb for 32-bit.  If you use the hugemem kernel,
the limit is moved to 64 Gb.  This is achieved by a feature that you
might have heard of called the 4Gb/4Gb split.  It provides for 4 Gb of
kernel space memory, then multiple blocks of 4 Gb user space memory.
This means, however, that if you have a single process with high
memory utilitzation, it will not be able to access more than 4 gb of
memory in the 32-bit world.  This is why large databases and J2EE app
server moved to 64-bit as soon as possible.

I would second your recommendation tho.  Unless you are unable to, or
its a big pain in the rear, switch to 64-bit for 4Gb+ memory.

On Jan 2, 2008 10:33 AM, Derek Konigsberg <octo at logicprobe.org> wrote:
> You could try a 64-bit distro of Linux, if possible, and see how that
> works.  I don't know the full technical explanation off-hand, but I think
> 32-bit x86 has a usable memory limit of around 3.5GB of RAM, even though a
> 32-bit address space covers 4GB.  (alternatively, I believe their is an
> additional feature called PAE for accessing more memory from a 32-bit OS,
> but not sure how to enable it, or if it is even supported on your
> hardware)
>
> -Derek
>
>
> On Wed, 2 Jan 2008, Randy Riley wrote:
>
> > My holiday present was 2 gig of additional memory to assist with machine
> > performance for virtual OS'es. Problem is Fedora only 'sees' 3362 meg of the
> > 4 gig installed (using FREE command). I checked in the BIOS and it does
> > recognize 4096 meg so I am confident the memory is functioning ok.
> >
> > I don't get it - does anyone know why Fedora (FC6) does this? Any way to get
> > it to recognize the 4 gig?
> >
> > TIA - Happy New Year
> >
> > --
> > Randy Riley
> > riley.rw at gmail.com
> >
>
> ---------------------------
> Derek Konigsberg
> octo at logicprobe.org
> http://hecgeek.blogspot.com
> ---------------------------
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>



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Kyle Gonzales
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