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Anonymous Mon 02 May 2011 04:48:00 No.17263158 View View Reply Original Report

Sorry if I'm making a stupid question. I'm not a Computer Science student.

But well. Virtual machines. Do they have to allocate memory and cache it all? Is it possible to make a virtualization program that uses the host RAM only when it needs to?

I'm making this question because whenever I open a Windows VM with 768MB of allocated memory, shit uses all those 768MB even if I'm running just Notepad++ and Windows 7, but taskmgr says that I'm only using 406MB.

Is it something proper of virtualization? Is it fault of VirtualBox? Is it even possible to use only the memory it needs?

Hell, am I missing something important here?

Am I missing something here?

Anonymous

Anonymous Mon 02 May 2011 04:50:00 No.17263195 Report

Quoted By:

Oh, yes, I forgot to make clear that I'm running a Linux host and a Windows 7 guest.

And the tl;dr: When I'm going to make a VM, I set the RAM to an specific value, but once it boots, it starts using all of it, even if it's there's nothing running in the VM asides from the OS itself. WHY.jpg

Anonymous

Anonymous Mon 02 May 2011 04:51:00 No.17263225 Report

Quoted By: >>17263251

Do your own homework

Anonymous

Anonymous Mon 02 May 2011 04:52:00 No.17263242 Report

Quoted By: >>17263275

I think the virtual machine needs to 'claim' the amount of memory allocated to it right when it starts up.

I don't think they can dynamically expand and contract the amount of memory they're taking.

Anonymous

Anonymous Mon 02 May 2011 04:52:00 No.17263251 Report

Quoted By:

>>17263225
How is this homework? I'm curious and i don't know too much about virtualization, asides from "OS runs in OS"

Anonymous

Anonymous Mon 02 May 2011 04:53:00 No.17263275 Report

Quoted By: >>17263296

>>17263242
>dynamically expand and contract the amount of memory they're taking
Yes, that was what I was asking.

Huh, is there any reason for this?

Anonymous

Anonymous Mon 02 May 2011 04:54:00 No.17263296 Report

Quoted By: >>17263316 >>17263505

>>17263275
it's because you touch urself at night

Anonymous

Anonymous Mon 02 May 2011 04:55:00 No.17263316 Report

Quoted By:

>>17263296
>urself
I thought easter break was already over

Anonymous

Anonymous Mon 02 May 2011 04:57:00 No.17263355 Report

Quoted By:

It's called dynamic memory allocation and it does exist, although I don't think it's available in your average virtualization software.

http://technet.microsoft.com/en-us/library/ff817651%28WS.10%29.aspx

Anonymous

Anonymous Mon 02 May 2011 04:58:00 No.17263380 Report

Quoted By: >>17263394

Fucking Hyper-V, how does it work

Anonymous

View Same Google ImgOps iqdb SauceNAO unknown.jpg, 16KiB, 634x571

Anonymous Mon 02 May 2011 04:58:00 No.17263394 Report

Quoted By:

>>17263380
>I'm running a Linux host

Anonymous

Anonymous Mon 02 May 2011 05:05:00 No.17263491 Report

Quoted By: >>17263495

>>17263158
The VM takes all the ram you assign to it when you run it.

Anonymous

Anonymous Mon 02 May 2011 05:05:00 No.17263495 Report

Quoted By: >>17263505 >>17264163 >>17264229

>>17263491
Yeah, but why? And does it have to be that way?

Anonymous

Anonymous Mon 02 May 2011 05:06:00 No.17263505 Report

Quoted By: >>17263520

>>17263495
See
>>17263296

Anonymous

View Same Google ImgOps iqdb SauceNAO unknown.jpg, 51KiB, 397x554

Anonymous Mon 02 May 2011 05:07:00 No.17263520 Report

Quoted By:

>>17263505

Anonymous

Anonymous Mon 02 May 2011 05:44:00 No.17264163 Report

Quoted By:

>>17263495
If it didn't, you could run yourself into a situation where suddenly they want more RAM and can't take it, having to dip into your page file.

Anonymous

Anonymous Mon 02 May 2011 05:48:00 No.17264229 Report

Quoted By: >>17264317

>>17263495
You'd have to code the client memory infrastructure differently to accommodate this. Memory management and allocation would be a mess, akin to hot-swapping memory on demand in very small increments.

Some OSes support this, and I presume there are hypervisor/guest combinations that do, but I doubt your run-of-the-mill desktop OS (on the client) does.

Anonymous

Anonymous Mon 02 May 2011 05:53:00 No.17264317 Report

Quoted By:

>>17264229
Err, I meant on the guest. Need more coffee.

The short answer is that it's much simpler for everyone involved this way, and most of the current hardware virtualisation implementations assume the memory structures (shadow page tables etc) remain relatively constant.

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