Re: Memory limitations in Linux.

From: Brian Gerst (
Date: Wed May 03 2000 - 10:08:42 EST

Nigel Jacob wrote:
> Howdy,
> Are there any plans to increase the max per process memory
> limitation in Linux 2.4 from 2GB(as in Linux 2.2.*)to 4GB(or more)?
> Is there a patch or maybe an (experimental) kernel in existance that
> supports 4GB or memory?

On 32-bit architectures, there is 4GB of virtual address space (per
process). Linux supports 3GB of userspace and 1GB of kernelspace
virtual memory. Older Linux kernels (2.2 and earlier) needed to map all
physical ram into the kernelspace virtual memory. Since room was also
needed for memory-mapped IO devices, this meant that only 960MB of
physical memory was supported. Linux 2.2 has an option to change the
user/kernel split to 2GB/2GB, which allows 2GB (minus MMIO space) of
physical memory. Linux 2.3 uses page table manipulation (and extensions
on recent processors) to access up to 64GB of physical memory, by not
needing to map in all memory all the time.

It may be possible to up the userspace to 3.5GB, but the absolute limit
is 4GB and the kernel still needs some space. If you really need more
than 3GB per process, you should look into using a 64-bit architecture.


Brian Gerst

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