[The Placid Casual]

I upgraded my G5 to just over 1 Gig Ram a few weeks ago, with all my stuff running it still had very little free memory at any on time (green on the pie chart in activity monitor icon)...This was confirmed in TOP. In fact, when I ran the same things on my Dual G4 450 box with the same amount of RAM, it had much more free. I have been really puzzled.

I just ran the iTunes update and a few others that were sitting in SUD and suddenly I have stacks more free memory... I mean loads. 1/3-1/2 of the chart free at any one time.

I know iTunes can hog resources but surely it couldn't account for 400MB+

Anyone any ideas what may have happened?

[bmedina]

Free memory is memory that is being wasted. Ideally, you want the system to have as little memory free as possible.

Thanks about it: you just spent a chunk of money on more RAM. Do you really want it sitting around doing nothing?

[The Placid Casual]

Well, I always thought of it as headroom for the apps I will need in the immediate/near future but am not using at that point in time...

It always disturbs me when there is no free memory and II have to open Sybase, VPC, Photoshop or something.

I'm not bothered by it at all, as my system is usually fit to burst when I'm working properly! Believe me, I think I must have the of the most hardworking G5's, it is literally never off and always doing intensive stuff!

It just seemed strange that there should be a big difference with no apparent cause.

[itai195]

Updates are an apparent cause... One of them may have fixed a memory leak that was affecting your system/apps.

[Big Mac]

Yeah, it is strange that your memory allocation changed drastically without any apparent cause. The only thing that I could think of is that you're looking at the graph at a different stage of memory allocation than you were previously. I imagine that you're basing your knowledge on information you saw after you restarted. Have you done any substantial work since then?

As the other poster pointed out (and as you probably already know) OS X caches a lot to memory in order to improve speed. Right now, I only have between 5 and 10MBs "free," 88MBs "inactive" and 183MBs "active." Based upon the knowledge that OS X makes efficient use of memory cache, one may intuitively infer that a large amount of free memory is undesirable. Most of the memory that would otherwise be free is presumably used to cache previous data and labeled inactive. The wonderful thing about a modern OS is that one doesn't have to worry about memory allocation anymore, since the OS handles all of it dynamically and automatically. Unless you're noticing significant slow downs or paging, you shouldn't really need to worry about memory.

[chris v]

There are four memory states: Wired, Active, Inactive, and Wasted.

Actually, I've forund that running the weekly cron script through Mac Janitor will free up inactive memory, if it's bugging you.

CV

[Madrag]

nice tip chris!
I tried the cron scripts with cocktail and it freed memory...

[larkost]

Madrag: you have just wasted resources on your computer and degrades its performance (ever so slightly) because you don't understand how memory works in a *nix environment. You would be much better off if you did not ever watch memory.

Here it is again for those of you who don't understand: Free Memory = Bad.

This might not be obvious to you, it may be anti-intuitive, but it is true.

[Madrag]

I've read this and other threads about the subject and understand that free memory can be bad, my point was that if I need to free it, I can, just by running the cron script.

Anyway, I don't see how I wasted soooo much resources, the cron scripts are maintenance scripts and they are executed anyway (if the mac is on all the time), as you might know...

[jamil5454]

Here's how *nix works:


As you use the computer more and more, the OS allocates more and more RAM to cache disk transactions and such. This is why it is always faster when you open a program the second time -- the OS has already cached some of the program in memory. The OS realizes that you have unused memory and so it uses it to cache many things, until you actually need memory for something. The OS then reduces the size of the cache to allow more memory for what you are doing. Thus, free memory isn't exactly BAD, it just means that you aren't doing anything to warrant your memory being filled up through caches.

So let's say you have 1gb of memory total, with only 200mb free, and ~400 set as "inactive". Then you open Photoshop. As Photoshop demands more and more memory, the OS will reduce the size of the cache and give it to Photoshop. Thus, you shouldn't really upgrade your RAM based on what you see in Activity Monitor, instead you should upgrade based on whether your system feels sluggish or not.

[msuper69]

This isn't OS 9.

Unix memory management has had decades to evolve into a finely honed piece of software.

Let it do it's job. Messing around with memory management outside of the Unix kernel is asking for trouble.