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Re: More than 2, but less than 3 GiB per process memory?

On Fri, 2005-09-23 at 14:45 +0200, Malte Cornils wrote:
> Hello,
> we've been trying to make a program (ITK/VTK image processing for a university 
> project) work. Unfortunately, the process needs slightly above 2 GiB of 
> virtual memory.
> Judging from the documentation I've seen, on 32bit systems I should be able to 
> allocate up to 3 GiB of virtual memory (1 GiB of 32bit address space is 
> reserved for the kernel).
> However, our test case for this terminates when trying to allocate more than 2 
> GiB of memory, even though we have a really big swap file.
> Does anyone have a clue why 2 GiB is the limit?

0GB-1GB  User space   - Used for executable and brk/sbrk allocations
                        (malloc uses brk for small chunks).
1GB-2GB  User space   - Used for mmaps (shared memory), shared libraries
                        and malloc uses mmap (malloc uses mmap for large
2GB-3GB  User space   - Used for stack.
3GB-4GB  Kernel Space - Used for the kernel itself.

>                                                  Would using a swap partition 
> instead of a swap file help? The 64G HIGHMEM kernel config option does not 
> seem to make a difference. On a real AMD64 system, the program works fine 
> with >2 GiB RAM, as was expected. Is there any way to make this work, besides 
> changing the algorithm to use less than 2 GiB of memory?


> We're using Debian sarge (3.1) with its provided 2.6.8 i386 kernels. Any hint 
> would be much appreciated!
> -Malte
> PS: Please Cc: me if possible

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