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Memory allocation and usage question

S

Shelton

macrumors member
Original poster
Feb 16, 2008
39
0
I am a recent switcher. Before I got my Mac Pro, I had used Windows my entire life. Mac OS X is an infinitely superior operating system. My productivity has increased ten-fold practically. OS X is a pleasure to use, whereas Windows is absolutely painful.

There is one thing I simply do not understand, though: Mac OS X's memory management. With 2 gigs of RAM, I was pretty regularly maxing it out, so I recently upgraded to 4. It has made a world of difference, but I still find myself maxing out my RAM and using the pagefile, yet I have 2+ Gigs of inactive RAM. Sometimes, I will have 3 gigs of inactive RAM, and my page outs will steadily increase. I just don't understand.

I searched Google and the forums, and it seems like inactive RAM is supposed to be freed up when needed, but that doesn't seem to be happening. Is this normal? Is there anything I can do to free up that "inactive" RAM, or is the easiest solution to just buy more?
 

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Inactive memory is not free memory, so it cannot just be re-allocated to another process. Inactive memory must be paged to disk before that can happen. In fact, I think that just before a chunk of memory becomes inactive, it is paged to disk so that another process can allocate memory from the inactive chunk without having to wait for paging.

Inactive memory will not be freed up since it has been allocated to a process. It is kept in memory in case that process tries to access it again, but it has also been paged to disk in case another process wants to allocate more memory. If that happens, the memory will be freed by the OS's memory management and allocated to the other process.

The fact that your machine sucks a lot of memory is not necessarily a bad thing, just as long as you don't have an excessive amount of page outs. So inactive memory is kinda like free memory, only there's a slight catch: it has been paged to disk in case another process wants to allocate more memory, and there is no reason for freeing up inactive memory before this happens.

It's been a while since I had my operating systems course at uni, so my knowledge about virtual memory is slightly rusty :eek:
 
Shelton said:
I am a recent switcher. Before I got my Mac Pro, I had used Windows my entire life. Mac OS X is an infinitely superior operating system. My productivity has increased ten-fold practically. OS X is a pleasure to use, whereas Windows is absolutely painful.

There is one thing I simply do not understand, though: Mac OS X's memory management. With 2 gigs of RAM, I was pretty regularly maxing it out, so I recently upgraded to 4. It has made a world of difference, but I still find myself maxing out my RAM and using the pagefile, yet I have 2+ Gigs of inactive RAM. Sometimes, I will have 3 gigs of inactive RAM, and my page outs will steadily increase. I just don't understand.

I searched Google and the forums, and it seems like inactive RAM is supposed to be freed up when needed, but that doesn't seem to be happening. Is this normal? Is there anything I can do to free up that "inactive" RAM, or is the easiest solution to just buy more?
Click to expand...

What's that process up the top with a frog-like thing next to it?
 
Infrared said:
What's that process up the top with a frog-like thing next to it?
Click to expand...

Azureus. It is such a ram hog. My last computer could barely run it; it would come to a grinding halt whenever I did heavy downloading. I never even notice it is running on the Mac Pro.
 
martinlk said:
Inactive memory is not free memory, so it cannot just be re-allocated to another process. Inactive memory must be paged to disk before that can happen. In fact, I think that just before a chunk of memory becomes inactive, it is paged to disk so that another process can allocate memory from the inactive chunk without having to wait for paging.

Inactive memory will not be freed up since it has been allocated to a process. It is kept in memory in case that process tries to access it again, but it has also been paged to disk in case another process wants to allocate more memory. If that happens, the memory will be freed by the OS's memory management and allocated to the other process.

The fact that your machine sucks a lot of memory is not necessarily a bad thing, just as long as you don't have an excessive amount of page outs. So inactive memory is kinda like free memory, only there's a slight catch: it has been paged to disk in case another process wants to allocate more memory, and there is no reason for freeing up inactive memory before this happens.

It's been a while since I had my operating systems course at uni, so my knowledge about virtual memory is slightly rusty :eek:
Click to expand...


Hmm. That means I need more RAM? I don't use many pro apps, but I do multitask heavily.

At what point do you not use virtual memory? Like, how much RAM would I need to hold me over for the next few years of computing, considering I don't use pro apps (photoshop) very often? I was hoping 4 gigs would do it.
 
Shelton said:
Azureus. It is such a ram hog. My last computer could barely run it; it would come to a grinding halt whenever I did heavy downloading. I never even notice it is running on the Mac Pro.
Click to expand...

Ah, thanks. It was the 80 thread figure that caught my eye.
 
Use transmission instead of Azureus :)

The thing with *nix operating systems, is the more memory you give them, the more they will use. Same with Windows, actually I'd say Windows is superior in this sense.
 
Shelton said:
Hmm. That means I need more RAM? I don't use many pro apps, but I do multitask heavily.
Click to expand...
Not necessarily. If you notice that your machine is paging a lot (lots of page outs), then you would benefit from adding more RAM. If not, then you're fine.

Shelton said:
At what point do you not use virtual memory? Like, how much RAM would I need to hold me over for the next few years of computing, considering I don't use pro apps (photoshop) very often? I was hoping 4 gigs would do it.
Click to expand...
Your OS always uses virtual memory. It's the fundamental principle of how memory is managed in a modern OS. If you ask me, 4 gigs is fine—especially if you don't run a lot of pro apps.
 
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