Dave Warren wrote:
Quote:
> In message <gv5748$usq$1@xxxxxx-september.org> VanguardLH
> <V@xxxxxx> was claimed to have wrote:
> Quote:
>>kellyapproved@xxxxxx wrote:
>> Quote:
>>> When you setup a guest OS, you need to allocate RAM to it.
>>>
>>> Let's say you have a host with 3 GB of RAM with two guests, each of
>>> which you allocate 1 GB of RAM.
>>>
>>> If both guests are in use, the host and two guests will get 1 GB of
>>> RAM each.
>>>
>>> Is there a way to set it so that if only 1 guest is in use, it can
>>> draw on the spare RAM that is allocated to the other guest that is not
>>> used.
>>
>>If one VM could monitor the memory usage of another VM to see what
>>blocks were unallocated, you just threw out the isolation that
>>virtualization is supposed to afford for security. >
> With all due respect, that isn't true at all. VMWare allows RAM to be
> over-allocated, which would be the first step to implementing this
> request.
>
> To avoid the performance implications of over-utilizing RAM, a second
> step would be to have the integration components/additions/tools report
> back the amount of available RAM within each VM to the host, and the
> host would reply back telling the additions to allocate or release RAM
> within each guest, tricking the guest into not using certain amounts of
> RAM to make that RAM available to the host (and therefore, for
> allocation to other VMs)
>
> Guests already communicate with hosts in a number of ways, adding a
> counters for available RAM, available clean pages, cache sizes and an
> API to the guest components wouldn't cause any sort of security issue if
> implemented properly. http://www.vmware.com/pdf/esx3_memory.pdf
It does talk about overcommitting the memory (i.e., having multiple
guests with a reserve specified for each whose total exceeds the real
memory for the host). It also mentions reallocation -- and that's where
they also mention clearing the reallocated memory to provide the
security of which I mention between those guests.
Allocating memory doesn't wipe it. Deallocating memory doesn't wipe it.
Whose going to do the wiping? In this case, the VMM has to do the
wiping and that means overhead. Their ESX product does that. Does
their free VMWare Server? I didn't see mention in VMWare Server's
manual that its VMM will reallocate and wipe memory between guests
(
http://www.vmware.com/pdf/vmserver2.pdf). I'm still reading but
reserve, overcommittment, and swapping are not reallocating wiped memory
from a pool to share amongst guests. Technologies employed in a
rebranded Connectrix variant that targets consumer-grade platforms
hardly equates with VMware's enterprise solutions for server-quality
hosts.
If anything like VMware's ESX memory sharing shows up in a Microsoft
product, I'd expect it to show up in their Hyper-V product, not in
something like VirtualPC. That's not to say Hyper-V has wiped memory
reallocation for sharing a memory pool across guests. I'm saying it's
no big surprise that VPC doesn't have it. Can reallocation between
guests be done? Yes. WILL it be done in VirtualPC? No, not without
such a massive overhaul that it isn't VirtualPC anymore, becomes an
enterprise-level product, and probably won't be free so we wouldn't be
discussing it here.