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Memory management question
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bernt
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Jan 7, 2007, 12:27 PM
 
I had Parallels running, using about 400 mb physical memory. Total available memory was about 20 mb. When I quit Parallels, the available memory jumped up to 1 gb, and not the expected 420 mb. Anyone care to explain this?

PS. I'm fully aware of the available vs inactive memory issue, so there is no need for yet another "a lot of available memory is wasted memory" lecture.
PowerBook 15" 1.25G/1G/80G | iMac G5 17" 1.6G/1.5G/300G | MacBook Pro 15" CD2.0G/1.5G/120G | MacBook C2D 2.2G/4G/160G
     
jasong
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Jan 7, 2007, 01:52 PM
 
I know I don't care to explain this.
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msuper69
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Jan 7, 2007, 01:56 PM
 
Why do we even care about memory?

As long as the system is running smoothly, there's no point to obsessing over RAM usage.
     
bernt  (op)
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Jan 7, 2007, 02:02 PM
 
Well, the thing is that my system does not run smoothly when only 20 megs are available. Constant page-outing is not a good thing, especially when you have a slow laptop harddrive. Also, it would be nice if someone could give a technical explanation for why my initial question.

And btw, jasong, why even bother answering, is it only for extra post counts?
PowerBook 15" 1.25G/1G/80G | iMac G5 17" 1.6G/1.5G/300G | MacBook Pro 15" CD2.0G/1.5G/120G | MacBook C2D 2.2G/4G/160G
     
Art Vandelay
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Jan 7, 2007, 02:52 PM
 
First, the 400MB of memory you've allocated is just for the guest OS itself. Parallels has to have its own chunk of memory just for the application itself. So, the Parallels process itself will always be more than 400MB. Second, there are several Parallels helper processes that are also running that will take up more memory.

However, the amount of memory freed up does sound a little high to even account for what I just said. If you're running the new beta version, that could account for it since they likely have a lot of debugging enabled. It's also highly possible that there's a memory leak too.
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jasong
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Jan 7, 2007, 09:40 PM
 
yes ;-)
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bernt  (op)
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Jan 8, 2007, 04:47 AM
 
Thanks, Art, I think you are on to something there.

But just to clarify, I have allocated 512 mb to the guest OS itself, it is the Parallels application (with the guest OS included) that takes up around 400 megs.

I might be because I'm running the latest beta of Parallels this happens, but I think I had the same behavior with the 1970 build. Anyone else have the same behavior?
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Chuckit
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Jan 8, 2007, 05:10 AM
 
As I understand it (and I'm not a low-level programmer, so I could be very much mistaken), how much memory can be freed at a time has to do with the actual mapping of memory. For instance, if memory for one program is stored alongside memory from another program and those pages get written to disk, that memory will be considered used but inactive until all of the memory in the file is released.

Frankly, memory management is such an arcane topic, I find it best not to think about it unless I'm actively trying to debug or optimize a program. Otherwise, my only concern is whether I have enough memory for the system to do what it wants.
Chuck
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