PAE kernel and 4GB of memory

Nifty Fedora Mitch niftyfedora at niftyegg.com
Thu Jul 24 21:40:21 UTC 2008


On Thu, Jul 24, 2008 at 01:49:34PM +0100, Howard Wilkinson wrote:
> 
> I am looking for a definitive answer to the question of where the PAE  
> kernels become useful. I have seen various articles that mention needing  
> PAE kernels if you have more then 4GB of physical memory in a 32-bit  
> processor environment. I have also seen statements that say you need  
> them if you have 4GB or more of memory. Now which is right? Also, even  
> if you need a PAE kernel because the last few bytes are not addressable  
> when you have exactly 4GB is this useful or is the trade off of larger  
> page tables and pages going to eat any benefit of being able to address  
> these few bytes and if so when does the PAE kernel become useful?
>

http://en.wikipedia.org/wiki/Physical_Address_Extension

Can you be more specific and define 'useful'.

In general on a 32 bit system you will have 32 bit pointers by default...
signed arithmetic gives you an effective 2GB process size.   Compare and
contrast lseek() and lseek64()... sizeof(off_t something).

But if you have six 2GB processes running on a 6.x GB system is that useful?
Are you playing with one Big process.

Do you have a test case  or pointer to a test case (best) so folks with
large memory systems can sanity test this for you?


-- 
	T o m  M i t c h e l l 
	Looking for a place to hang my hat.




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