Re: mmap'ing a large file

[Gianni Tedesco]

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On Wed, 2002-08-14 at 16:42, Mike Black wrote:
> Is there a logical reason why a process can't mmap more than a 2G file?
>=20
> I seem to get stuck at 2142208000 with
> mmap: Cannot allocate memory

Perhaps this should be an FAQ item.

Intel is a 32bit architecture, that is to say the address space is 2^32
bytes (4GB), of this address space the kernel takes the top 2GB and
userspace the bottom 2GB.

There are patches that allow userspace to have 3GB or even 3.5GB
floating around. Obviously the kernel then only has 1GB/512MB - I'm not
sure what affect that will have.

The workaround to this is to only map in the portion(s) of the file you
actually need dynamically but this isn't always simple depending on the
application.

I suppose the short answer is 'its a hardware problem'.

HTH

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// Gianni Tedesco (gianni at ecsc dot co dot uk)
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