Re: address space reservation functionality?

["Robert W. Fuller" <orangemagicbus@sbcglobal.net>]

Arjan van de Ven wrote:
> On Mon, 2005-01-10 at 15:52 -0500, Robert W. Fuller wrote:
> 
>>Hi,
>>
>>I was wondering if some functionality existed in Linux.  Specifically, 
>>in Solaris, you can mmap the null device in order to reserve part of the 
>>address space without otherwise consuming resources.  This is detailed 
>>in the Solaris manpage null(7D).  The same functionality is also 
>>available under Windows NT/XP/2K by calling the VirtualAlloc function 
>>with the MEM_RESERVE flag omitting the MEM_COMMIT flag.  Does Linux have 
>>a similar mechanism buried somewhere whereby I can reserve a part of the 
>>address space and not increase the "virtual size" of the process or the 
>>system's idea of the amount of memory in use?  I could not find one by 
>>using the source.
> 
> 
> malloc() already does this...
> what you describe is the default behavior of linux; only when you
> actually write to the memory does it get backed by ram.
> 
> 

Sorry about the top posting.  This is a resend without it.

This is not quite the same thing.  This still does a check for whether 
or not there is enough memory and includes this in the virtual size of 
the process.  I simply want to reserve a part of the address space so 
I'm guaranteed I can map something else over a contiguous portion of the 
address space.  I don't want it to check for available memory or 
increase the virtual size of the process because I will be using this 
region sparsely.  That is why Solaris and Windows have separate 
interfaces for this.