Re: large memory support for x86

From: Ingo Molnar (
Date: Thu Oct 12 2000 - 16:42:07 EST

On Thu, 12 Oct 2000, Timur Tabi wrote:

> Of course, you could define a pointer to be a 48-bit value, but I
> doubt that would really work.

no, x86 virtual memory is 32 bits - segmentation only provides a way to
segment this 4GB virtual memory, but cannot extend it. Under Linux there
is 3GB virtual memory available to user-space processes.

this 3GB virtual memory does not have to be mapped to the same physical
pages all the time - and this is nothing new. mmap()/munmap()-ing memory
dynamically is one way to 'extend' the amount of physical RAM controlled
by a single process. I doubt this would be very economical though.

Such big-RAM systems are almost always SMP systems, so eg. a 4-way system
can have 4x 3GB processes == 12 GB RAM fully utilized. An 8-way system can
utilize up to 24 GB RAM at once, without having to play mmap/munmap
'memory extender' tricks.


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