Page Fusion

[HeavyThumper]

I have several Windows XP 32-bit guests. I have run "VBoxManage modifyvm <guestname> --pagefusion on" for each of them. I'm running 64-bit Ubuntu Linux. I have installed 3.2.4 guest additions.

I don't see any evidence of any memory sharing - including VBoxManage metric output. Did I miss a step to enable pagefusion?

Are host CPU hardware virtualization extensions required for page fusion?

[Perryg]

See Chapter 4.9. Page Fusion in the VirtualBox users guide.
VirtualBox online users manual

[HeavyThumper]

I appreciate the manual reference - but I did read it previously. I did not find any mention of hardware virtualization requirements, nor any additional steps beyond those I mentioned - which is why I asked the question. So I'm still asking - why isn't it working?!

[Perryg]

Well I am at a loss why it is not working for you. I have Ubuntu 10.04 64-bit and (2) XPpro 32-bit and it works on them. When you ran the metric query did you use the switches that the manual shows?
My host has an Intel core2 duo. What are you using?
Run VBoxManage showvminfo "<vm name>" and make sure that page fusion shows it is on.

I am using VirtualBox 3.2.6-B2 but I believe that it worked in 3.2.4 for me. Versions seem to all run together these days since they come out so fast so I can't swear to it.

[HeavyThumper]

I did use the switches - saw nothing. Also no change in host memory consumption.

My host is using a pair of Opteron 265's - first generation Opteron so no hardware virtualization support.

[Perryg]

Ah you missed the note at the bottom of the section in the users manual.

<snip>
Note
VirtualBox supports Page Fusion only on 64-bit host operating systems. Mac OS X hosts are currently not supported. Page Fusion is only available for Windows 2000 and later guests with current Guest Additions.
</snip>

[HeavyThumper]

Where is it said that 64-bit Virtualbox Hosting requires hardware virtualization?

[Perryg]

Never mind I was ready this all wrong. I still have no clue why it works for me and not for you.
Have you posted a ticket at bugtracker yet?

[Soulatial2]

I tried pagefusion.
Host is Win7 64 Bit 16 GB RAM.
However page fusion is not very efficient. On Win 7 32 Bit as Guest and 2 instances, it shares only 57 MB with a usage of over 1 GB RAM each machine. The machines are clones, windows is just started, nothing else opened, so there should be much more memory to fuse. Configured Memory is 1,5 GB for each.

With 64 Bit guest it can share 150 MB which is still very low, as both machines are clones and just started with nothing else. Overtime it seems to rise, currently it is 200 MB.

With 2 XP Clones and 1 GB of RAM it is 60 MB which are shared. First I thout it is ASLR http://en.wikipedia.org/wiki/ASLR which makes memory re-usage so low under 7 guests, but it is under XP as well and this OS does not have this feature.

To query the memory usage use vboxmanage.exe metrics query <your vm name>
you have to enable it with VBoxManage.exe metrics setup --period 1 --samples 2 <your vm name>
The Value under Guest/RAM/Usage/Shared is the value

With VBoxManage.exe metrics setup --period 1 --samples 2 host
and vboxmanage.exe metrics query | more you get under RAM/VMM/Shared the total shared memory. I have 312 MB with 6 VMs running (Win 7 32-Bit, Win 7 32-Bit, XP 32-Bit, each twice of course). I consider this very low as they are clones and just started. Perhaps shared memory increases when you use the VMs longer.

[noteirak]

FYI, this post was more 2 years old and nothing is relevant anymore. Don't wake the dead

As for the page fusion, Virtualbox use a specific algorithm to find pages but this algorith hasn't been improved for a while, due to the lack of interest of this for the main category of Virtualbox Users. (This was the comment given by one of the devs).
Also, there is a bug with page fusion : Bugtracker ticket, so it shouldn't be used for now.