Over 3GB of swap files with 16GB of RAM?

megagram wrote:

K as far as I understood modern OS's, they write memory to disk when physical RAM is exhausted. My physical RAM has not been physically exhausted and yet I still see high numbers of pagefiles. This is my concern; especially since I have an SSD that can't be replaced I'd rather not accelerate its demise with unecessary writes.

That's the thing - it is way more complicated than that. That is how virtual memory worked 20 years ago. It is best to avoid looking too closely at memory values. When people do that they start seeing problems that aren't there.

I'm not sure how you can say mountain lion's virtual memory is optimized for SSDs and that most of the swap space doesn't exist, even though it exists in the form of pagefiles without backing it up with concrete sources.

I say that because Apple is moving to SSDs for their new machines, so that is where the focus is. Even with 16 GB, any application could exhaust your memory if allowed. MacOS X uses those swap files to keep that from happening.

I doubt you will have any luck stressing Mountain Lion's VM system. While running Xcode heavily I have been able to get my free RAM to less than 10 MB, but it recovered right away with no noticeable performance impact.

You really don't need to worry about "swap used". I was unable to find a clear definition of entirely what this value represents. There are a number of possibilities, any or all of which are plausible. It could be memory-mapped files that are on disk to begin with but are now considered to be in memory. They could be initialization code like shared libraries that are in the application memory space but are shared. Therefore, there is no need to duplicate them in RAM. They can be permanently swapped to disk. They could be backing store of the application such that if it does need to be swapped, the OS doesn't have to worry about writing it. I don't know the real answer.

I wouldn't worry about it unless you're seeing a corresponding performance hit. If you are, then if you can reproduce it consistently, that might be worth filing a bug about or something. Otherwise, it is probably just writing cold pages out to disk for performance reasons.

Well I *am* seeing a slowdown. With Snow Leopard there were 3 swapfiles totalling 256 M Bytes. With Snow Leopard there are 6 files totaling 2 G Bytes, and I have seen this go up to 7 files and 3 G Bytes. And I do not have a lot running. Free memory is usually pretty low as reported by top, a few hundred MBytes. I have 4 G of RAM. Unlike Snow Leopard, these swapfiles never go away even after quitting applications. Applications were slow to launch as swapfiles were being written to or read from. I think Mountain Lion has a serious virtual memory problem.

I beg your pardon. It takes unnaturally long to launch an app and I look at the 1G swapfile and see that this one and the others have just been updated and you tell me it is unrelated? Sorry. Writing to disk is relatively slow.

Nathan Goldshlag wrote:

Writing to disk is relatively slow.

Why is that? We all have the same disks and operating systems, but only you are complaining about unnaturally long times to launch. Perhaps your disk is failing.

I'm constantly checking Activity Monitor and "Free RAM" is always around 8GB or more

Meaningless information.

An application could spike its memory usage, then go away giving back all the memory. You could have been running a backup which was filling the memory with cached data, while another app(s) was in need of memory then things quieted down.

You cannot be working AND watching Activity Monitor full time, and Activity Monitor is ONLY showing you free memory for the moment you are looking at it.

If you want to track free memory over time, then start am Applications -> Utilities -> Terminal session and run a command such as:

vm_stat 60

which will watch the VM statistics and report them every 60 seconds (change the time interval if you like, but make sure your Terminal scroll back is sufficient (and if it is set to "available memory" keep in mind that if you allow this to run long enough, Terminal will suck up all your RAM 🙂 ).

Then if vm_stat never reports your free space AND inactive space as going low together, then you might have an issue.

HOWEVER, if you have an app that uses anonymous memory mapped pages as a way to communicate between processes (such as a browser that uses separate processes for each TAB, but keeps the pages and images in a common cache of mapped memory, then this anonymous memory mapped area is frequently backed by the /var/vm/pagesfiles.

There are a host of reasons why Mac OS X might allocate /var/vm/pagefiles, but never use them or use them briefly.

megagram wrote:

And all "Swap used" means is the amount of hard disk space that is used up by the various swap files in /var/vm. Quite simple.

I actually went out of my way to track down the answer to a valid question that has been asked before. I made a point to avoid giving you such a simplistic answer.

But, as I"ve mentioned in another reply, it was a font issue causing the fontworker process to consume lots of memory.

But seriously, I think you need to refresh what you think you know about virtual memory before coming into these forums and claiming a bunch of nonsense.

And as I mentioned earlier, virtual memory is Mountain Lion is highly optimized. Anyone who dwells on it looking for a problem where there is none is going to accomplish nothing but waste their time. Had you not been so concerned about perfectly normal readings in Acitivity Monitor, you might have found the problem in less than four days.

In the future, if you have a specific problem like a hanging system right after waking from sleep, do us all a favour and mention that at some point. 🙂

megagram wrote:

I did mention that I had a problem with hanging right after waking from sleep. I guess you weren't paying attention.

That was in your 6th post, a reply to my question, in the first 5 posts you did not mention it, I think you are being a bit too dismissive of etre's attempts to help with a problem vaguely described. Happy that you found the answer to the 'hanging' issue.

megagram, I agree with you. etresoft has been slinging some misinformation. I did not have any fontworker process, nothing spiking my CPU, and yet when the big swapfiles were being written to my machine ground to a crawl. Today upgraded from 4 to 8 G of memory, still not as much as you. We'll see how it goes.

megagram wrote:

True. My point is his attempts at helping were not helpful at all given the fact that almost everything he said about VM was wrong.

I will not say anything here on Apple Support Communities unless I know it is true. If I need to guess or speculate to pacify someone who won't take an answer (as in this case), I will qualify my answer (as I did in this case).

I had no idea what the problem was. There is a problem when you have 3GB+ of swapfiles on a machine with 16GB of RAM and a light workload.

Until a couple of hours ago, you had not indicated that there was any problem with your system. You were asking a question about virtual memory. I told you to ignore virtual memory because "If you are having problems, the cause is elsewhere" - as it was. If you have bad fonts and some process running out of control and exhausting 16 GB of RAM, you do not have a "light workload". Obviously you weren't "constantly checking Activity Monitor" either. I should have noticed a statement that suspicious. Oh wait, I did.

Had I listened to etre I would not have solved my issue.

To redundantly repeat myself - if you have an issue - say so. You can't post a screenshot from Activity Monitor with values on it that are identicial to 2 million other machines and expect anyone to get worked up over it.

etresoft, you continue to misinform people here and claim there is not virtual memory problem. I had no font problem like megagram, yet relatively quickly got huge swapfiles and the system was unresponsive and slow to launch applications. When I said the disk accesses are relatively slow you just poo-pooed it. Sorry but the reason things were slow as writing to these swapfiles. This is how virtual memory works - when you run out of physical memory stuff gets written to disk so that applications can access large memory spaces. In my case I was not running a lot of stuff.