understanding applications and PAE

[Nathan Bryant]

Sounds like you could treat /dev/shm as a large, linear file and mmap() 
one window into it at a time...

Chris Kloiber wrote:

>On Tue, 2003-12-09 at 08:16, James Olin Oden wrote:
>  
>
>>On Mon, 8 Dec 2003, Vanco, Don wrote:
>>
>>    
>>
>>>While I hate to use this as a support line I've gotten no help from the 2
>>>local lugs I've queried, and know that there's some heavy hitters lurking
>>>here.
>>>
>>>I understand that the Linux kernel can (through PAE) provide memory paging
>>>beyond 4GB of physical memory on 32-bit architecture.  What I need to
>>>understand is: what are the requirements on the application side to utilize
>>>this memory?  I'm looking for documentation / links that talk about
>>>applications and PAE.
>>>
>>>Case in point: Lotus Notes on OS400 can address huge amount of RAM, but when
>>>it's running on Linux does it need to be compiled in a specific manner, or
>>>with some specific bit of code / API to address more than the architecture
>>>physically supports?
>>>
>>>      
>>>
>>Hi Don,
>>
>>We use the PAE feature where I work.  The deal is that this functionality 
>>only makes it possible for the kernel to access and use all this memory,
>>but each process still can only address 4Gig of memory less the amount of
>>memory under 4Gig the kernel is using.  If you wanted a single app
>>to use more than 4Gig, at this point you would need to create several
>>processes that share memory.  Even this this is very specific to the 
>>application as to whether such a scheme could be used effectively (you
>>would in effect be shuffling data around processes as needed).
>>
>>Does anyone know of any other solutions than PAE?
>>    
>>
>
>Can you do some tricks like Oracle does? They can use very large shared
>memory segments using /dev/shm I've seen customers use /dev/shm up to 6
>gigs on a 8 Gig box, and 14 Gigs on a 16 Gig box. This is probably
>slower than normal ram access, but faster than swapping to disk.
>Remember I'm in Support, I can't help you program this.
>
>  
>

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