Mailinglist Archive: opensuse (3605 mails)

[Per Jessen <per@xxxxxxxxxxxx>]

James Knott wrote:

> We're not talking about virtual memory here, which is an entirely
> different thing.  Virtual memory is the process for making disk space
> appear as actual memory. 

But we are talking about an application accessing memory, which on Linux
is done exclusively through the virtual memory manager.  That the VMM
will use the PAE for addressing up to 64Gb of physical memory does not
concern the application. 

> On 32 bit computes, a process can normally access only a 4 GB range. 
> PAE allows access to more than that range, 
[snip]
> In order to use that greater range, an app has
> to use the PAE API to instruct the OS to make that memory beyond 4 GB
> available.  If the app doesn't use PAE, it can't go beyond the basis 4
> GB.

OK - do you know how this is done on Linux?  I'm really curious as I've
always considered this kernel-only stuff.  I have no problem with the
concept of mapping physical memory (normally not used by the kernel)
into my own address-space, I just did not think Linux provided that
option.  

My understanding of Linux' use of PAE is that enabling CONFIG_HIGHMEM64
essentially  makes the kernel switch to a three-level instead of a
two-level address lookup. 


/Per Jessen, Zürich


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