Re: large memory support for x86

From: Tigran Aivazian (
Date: Thu Oct 12 2000 - 13:13:27 EST

On Wed, 11 Oct 2000, Kiril Vidimce wrote:

> Hi there,
> I am trying to find out more information on large memory support (> 4 GB)
> for Linux IA32. Is there a document that elaborates on what is supported
> and what isn't and how this scheme actually works in the kernel?
> My primary concern is whether a process can allocate more than 4 GB of
> memory, rather than just be able to use more than 4 GB of physical
> memory in the system.
> Also, I see that the highmem support is just an option in the kernel.
> Does this mean that there is a significant performance penalty in using
> this extension?

Linux does support 64G of physical memory. My machine has 6G RAM and runs
absolutely nice and smooth as it should. Everything "just works" (ok, not
counting a few subtle cache-related issues and stability of PCI subsystem
but those happened many hours ago and were quickly fixed so they are
history now and therefore long forgotten ;).

As for PAE, yes it does incur penalty of about 3-6% of performance
"overall". By overall performance I meant the unixbench numbers. I have
published the numbers comparing PAE/4G/nohighmem kernels on the same
machine sometime ago...

So, it only makes sense to enable PAE if you have more than 4G of memory.


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