Tom Austin <taustin> wrote:

> Ger wrote:
>> When trying to run a render that uses over 3Gb memory I get this error
>> 
> 
> ...
> 
> 
>> Keeping it below 3Gb (by reducing the number of lights) it works fine.
>> 
>> Just wondering if I should keep that 3Gb limit in mind or if there is
>> something else going wrong.
>> 
>> Running:
>> Athlon 64x2 3800+
>> 4 Gb mem internal (6Gb swap) (so available mem should not be a problem)
>> Suse 10 with Linux athlon64 2.6.13-15-bigsmp kernel
>> Self compiled Povray 3.6.1
> 
> It looks like you know what you are doing, but here are some things I
> have run across regarding memory - based on 32 bit systems.
> 
> A single application (thread) is limited to using 2GB or 3GB depending
> on your OS and settings within the OS.
>
> I have found that typically in 
> Windows the limit is 2GB and Linux is 3GB (tho these can be affected by
> OS settings).  I have run into these ceilings myself running various
> applications.  I have found no way of allowing for more memory usage in
> a 32bit system.  I set up 16GB swap once only to have the application
> crash at 3GB.

This is most likely due to limits inside the application, not the OS

> 
> Also, the OS might be capable of using much more than 2GB (or 3GB), but
> it must be in the form of separate applications (or threads).  It might
> be entirely possible to run (3) 2GB applications - 

I'm currently running 2 renders of 2.5 Gb each, alongside the usual bunch of
office thingies, mail, news, browsers, photo editors, etc etc.
Swap space usage is upto 3.5 Gb now.

> tho I have not tried 
> or tested this myself.  Others here with more knowledge can set me
> straight.
> 
> I remember that these is a configuration within Linux that allows it to
> use different memory mapping to allow for large memory usage.  If I
> remember correctly, it was a kernel option and required the kernel to be
> recompiled.

Correct, when you go above 3 Gb you will need to change the kernel to the
"big" version allowing for more internal memory, and this is where my
problems started. It turned out that something fishy had happened when I
switched kernels.

> 
> If your system is 64 bit, it could be that something is still limiting
> it to using 32 bit memory addressing.

Not under Linux, I don't know about 64bit Windows

> 
> Now, my experience is only with a 32 bit system.  I understand that 64
> bit systems have much different limitations, but I have no experience
> with them.  I hope that this sheds a bit of light for you.
> 

With the arrival of 64 bit systems the phrase "The sky's the limit" has been
superseded with "The sky's just the beginning" :)

> 
> 
> 
> LAter... Tom

-- 
Ger

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