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List:       vbox-users
Subject:    Re: [vbox-users] assigning more memory to the guest than exists on
From:       Paul Gilmartin <Paul.Gilmartin () Sun ! COM>
Date:       2008-12-28 17:31:11
Message-ID: 19CF84C0-722A-4B64-9DFA-3C92AF9CAB6A () Sun ! com
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On Dec 28, 2008, at 09:17, Frank Mehnert wrote:

> Greg,
>
> On Wednesday 24 December 2008, Gregory Nowak wrote:
>> The subject pretty much asks my question. Is it possible for me to  
>> run
>> a guest os in vbox, with more ram assigned to it than is on the
>> physical host, (I.E,.. run a guest with 800Mb of ram on a host that
>> has 512Mb of ram)? In theory, this should be possible on a gnu/linux
>> host, provided I have enough swap. How about on a windows host?
>
> I would suggest you not to try that. The guest will run fine as long
> as it does not touch all physical memory it needs. For instance,  
> Windows
> will touch all memory during boot. As a result your VM will be paused
> and you will get a message box explaining that the guest is currently
> stopped and you have to free more memory.
>
In fact, my experience with OS X on a 1GiB MacBook when I assigned
768 MiB to the guest leaving only 256 MiB for the host was that
the guest may have been running fine but the host choked for
memory shortage.  No message ever appeared; if it had the host
would have been too paralyzed to allow me to act on it.

> Note: As soon as a block of physical memory of the host is assigned to
> the guest, it is marked as non-swappable and it will not be freed  
> before
> that VM finished. This will be changed in future versions of  
> Virtualbox
> (e.g. ballooning).
>
I wondered about that.  Ugh.  Double-swapping.  The best tactic might
be to assign an enormous amount of memory to the guest so the guest
never swaps; the host does it all.  But what would happen when the  
guest,
for whatever reason, marked a block non-swappable?

-- gil


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