Re: allocate more than 2 GB on IA32

[Hartmut Manz]

On Tuesday 11 February 2003 17:11, Martin J. Bligh wrote:
> > i would like to allocate more than 2 GB of memory on an IA32
> > architecture.
> >
> > The machine is a dual XEON_DP with 3 GB of Ram and 4 GB of swap space.
> >
> > I have tried with the default SUSE 8.1 kernel as well as with a
> > 2.4.20-pre4aa1 Kernel compile by my own using these Options:
> >
> > CONFIG_HIGHMEM4G=y
> > CONFIG_HIGHMEM=y
> > CONFIG_1GB=y
> >
> > but I am only able to allocate 2 GB with a single malloc call.
> > I tought it should be possible to allocate up to 2.9 GB of memory to a
> > process, with this kernel settings.
>
> Well, assuming you had no user-space code or data, or a stack, or any
> shared libraries to fit into that space as well ;-)
>
> Try shifting TASK_UNMAPPED_BASE down from 1GB to 0.5GB - that should give
> you some more breathing room, though you'll never get to 2.9GB.
>
> M.

First of all I would like to say THANK YOU for your help.

I am now able to allocate up to ~3.2 GB of memory on a 4 GB Machine, even with 
shared libraries. 

This is what I have done.

1. I have activated the kernel option in  Kernel 2.4.21pre4aa3
   CONFIG_05GB=y
  This gives the following: 
    a: TASK_UNMAPPED_BASE is now 0xe000000 wich is  224 MB
    b: Upper Limit for User-Space memory is now at 3.5 GB
   So I have the potential to allocated up to 3360 MB of memory

2. I have exchanged malloc with anonymous mmap, since malloc
    was still only able to allocate about 2 GB.

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