[Vm-dev] Question about memory allocation in VM

[Andreas Raab]

Look at memory mapping (mmap on unix, MapViewOfFile on Windows). What 
you're describing can be done simply by mapping and unmapping memory 
regions from an image file. I believe the iPhone does just that.

Cheers,
   - Andreas

On 5/4/2010 6:12 AM, Mariano Martinez Peck wrote:
> Sorry in advance if this was asked before...I have something in my mind
> that says it was :(
>
> I want to know how the memory is allocated between the VM and the OS.
> For example, I know (actually, I think I know) that in Mac OS VM when
> you run an image, the VM allocates (malloc() I guess) the same size at
> least, of the image. So...I couple of questions:
>
> 1) Is the same behavior for all OS ? If not, which happens with the rest?
>
> 2) Where is such behavior defined? I don't think it is in VMMaker but in
> the C support code of each VM. But where (.c and function anme) , any
> quotes?
>
> 3) In am working (actually yet thinking) a mechanism that will probably
> use much less memory than the image. The idea is to swap to disk unused
> objects. Then....the amount of memory I will use should be MUCH smaller
> than the size of the image. So my question is, which changes should I do
> to the VM so that it uses only THAT amount of memory and not the size of
> the image.
>
> As I said, suppose I have an image size (in disk) on 15MB. Suppose I run
> that image, and then, as I swapped a lot of objects to disk, the actual
> usage of memory is 3 MBs. So what I want is that OS only uses 3 MB and
> not 15. Can I do that ?
>
> Thanks a lot for answering to this newbie :)
>
> Mariano