Parallels Memory handling

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bash103

Bit poster
This is probably a very stupid question, but I have to ask. Does Parallels reserve the amount of memory you define for a VM? Or does it only grab it when you actually launch the VM? For example if I have 2GB of memory installed and assign 1GB to Windows XP Pro through Parallels does it actually take/reserve the memory from the Mac side, or does it only allocate the memory when the VM is actually running. Therefore the Mac side has the full 2GB unless I lauch the VM.
 
I can't say for certain, but since no one else wrote anything, I figure I'd throw my 2 cents in. I use the iStat nano widget (props to that developer!) and I believe I only notice the memory filling up once I launch one of my virtual machines.
 
I can't test this right now since it's inconvenient to reboot, but here's how to find out:

1) Reboot your Mac
2) Start Activity Monitor
3) Select System Memory, and observe allocation.
4) Start Parallels, and observe allocation.
5) Start your VM and observe allocation.

Note that available (unassigned) memory is the sum of free and inactive.

6) Post the result for the curious among us.
 
Remember that Mac OS X uses Virtual Memory, so I would guess that it allocates as much as you configure it for. Then IF the memory is needed by the VM that Parallels is running, it will be available first from that real memory.

What you see in Activity Monitor should confirm that it uses UP to that amount of free memory, if it needs to.
 
bash103 said:
This is probably a very stupid question, but I have to ask. Does Parallels reserve the amount of memory you define for a VM? Or does it only grab it when you actually launch the VM? For example if I have 2GB of memory installed and assign 1GB to Windows XP Pro through Parallels does it actually take/reserve the memory from the Mac side, or does it only allocate the memory when the VM is actually running. Therefore the Mac side has the full 2GB unless I lauch the VM.
Click to expand...

Ok, I just did a test, Im running dashboard widget called iStatNano

1. I shut down Parallel and noted the memory,

- wired = 237mb
- inactive = 475mb
- free = 757mb
- active = 559mb
- used = 1.24gb
- swap = 512mb

2. staring parallels without starting guest OS

- wired = 239mb
- inactive = 604mb
- free = 622mb (Remember Parallels takes 96mb regardless)
- active = 563mb
- used = 1.37gb
- swap = 512mb

3. Booted into Guest host, (note i have my Parallels set to use 800mb for all VMs

- wired = 802mb
- inactive = 619mb
- free = 36mb
- active = 568mb
- used = 1.95gb
- swap = 512mb

Your milage may vary but you can use the value to come up with your answer ;-)
 
Last edited:
PTWithy said:
And when you _quit_ Parallels, do you get your wired memory back? I seem not to. This is a bug.
Click to expand...

The guy who wrote PDTweaker (http://www.multisolar.com/software/PDTweaker/ ) suggested to me that it is compatible with build 1970, and that PDTweaker it MIGHT help with some of the bad memory use problems. I'm too busy to try it today, but maybe someone else could, and report back?

[The problem if it exists, and if PDTWeaker fixes it, is that Parallels has opened the HDD (virtual disk drive) file in the wrong mode, so OSX decides that it's very important to try to cache as much of it in RAM as possible. Since your average HDD file is > 2GB, this basically means that after a while, OSX will have swapped all your other programs out to disk...]
 
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