[Vm-dev] Question about memory allocation in VM

[Igor Stasenko]

On 4 May 2010 16:12, Mariano Martinez Peck <marianopeck at gmail.com> 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?
>
Windows using VirtualAlloc, and Linux - mmap. Both allocating a
virtual memory, not malloc().
For macs, i don't sure, since i don't have mac :)

> 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?
>
platforms/win32/vm/sqwin32alloc.c
platforms/unix/vm/squnixmemory.c
platforms/Mac OS/vm/sqmacmemory.c

> 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.
>
you certaintly will need the virtual memory, so you can swap unused
pages to disk.

> 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
>
>



-- 
Best regards,
Igor Stasenko AKA sig.