How FreeBSD manage more than 4GB on 32 bits architecture

[Adrian Chadd]

On 9 April 2015 at 09:58, Valeri Galtsev <galtsev at kicp.uchicago.edu> wrote:
>
> On Thu, April 9, 2015 11:19 am, Adrian Chadd wrote:
>> Hi!
>>
>> This sounds... very exciting. I'd start by taking a look at how PAE
>> works - you may be able to reuse all those pieces and just implement
>> more than the 4 bits of physical address space. The interesting bits
>> of PAE aren't just the extension of the physical addresses, but all
>> the management of mapping things into virtual address space as
>> required.
>
> The only problem with all these exercises is: on 32 bit CPU box a single
> process still can only have 4GB of address space (according to my
> definitely not deep enough knowledge of kernel)...

Well, whatever the kernel/user split is, sure.

For some workloads that's fine; you just can't mmap a TB of memory.
But there's nothing stopping you mmap'ing windows into a larger
physical address space. I've done that before to get around
limitations.




-adrian