1 2 3 Previous Next 73 Replies Latest reply: Jun 23, 2013 9:25 AM by chef098
megagram Level 1 Level 1 (90 points)

Just bought a MBPr with 16gb of RAM (more for futureproofing than any actual need right now). I'm constantly checking Activity Monitor and "Free RAM" is always around 8GB or more. I notice, however, that the "Swap used" totals are quite high. I don't have any pageouts so why do I have so much swapspace being consumed? With an SSD drive in here, should I not be worried that the OS is using swapspace so much when it probalby doesn't need to?

 

Thanks!


MacBook Pro (Retina, Mid 2012), OS X Mountain Lion
  • 1. Re: Over 3GB of swap files with 16GB of RAM?
    etresoft Level 7 Level 7 (24,270 points)

    Constantly? I wouldn't worry so much. Virtual memory in Mountain Lion is highly optimized - especially for SSD drives. Much of that swap space doesn't really exist. There is sophisticated fakery going on underneath to keep RAM-hungry applications from allocating memory they aren't really using.

  • 2. Re: Over 3GB of swap files with 16GB of RAM?
    Csound1 Level 8 Level 8 (35,455 points)

    Do you have a virtual machine installed (Fusion, Virtual Box etc)?

  • 3. Re: Over 3GB of swap files with 16GB of RAM?
    megagram Level 1 Level 1 (90 points)

    Do you have a source for that information? I would love to read about it.. Thanks.

  • 4. Re: Over 3GB of swap files with 16GB of RAM?
    etresoft Level 7 Level 7 (24,270 points)

    megagram wrote:

     

    Do you have a source for that information? I would love to read about it.. Thanks.

    It is pretty standard practice for modern virtual memory systems. I have no idea where I saw it specifically. It was probably some developer documentation. Apple isn't doing anything particularly special. Pretty much all modern virtual memory systems work the same way. It is just that no other people obsess over the details like Mac users do.

     

    I can tell you that you should ignore any suggestions or adivce to try to change virtual memory in any way. As a developer, I have been running Mountain Lion for some time and using it heavily with Xcode. The virtual memory system in Mountain Lion is the best I have ever seen. There is nothing an end user can do to improve it - only damage it. If you are having problems, the cause is elsewhere.

  • 5. Re: Over 3GB of swap files with 16GB of RAM?
    megagram Level 1 Level 1 (90 points)

    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.

     

    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. Thanks, anyway.

  • 6. Re: Over 3GB of swap files with 16GB of RAM?
    Csound1 Level 8 Level 8 (35,455 points)

    How about answering my question?

     

    See Below

  • 7. Re: Over 3GB of swap files with 16GB of RAM?
    megagram Level 1 Level 1 (90 points)

    Sorry I missed your question. I have VirtualBox installed but do not run it often (and when I do my VM only has 1GB allocated). As I say, my "free" memory in activity monitor never goes below ~8GB. I've been using Mac OS X since the 10.0 and am very familiar with the swap system. I'm just surprised to see any swapfiles when my memory usage is very minimal.

  • 8. Re: Over 3GB of swap files with 16GB of RAM?
    etresoft Level 7 Level 7 (24,270 points)

    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.

  • 9. Re: Over 3GB of swap files with 16GB of RAM?
    Csound1 Level 8 Level 8 (35,455 points)

    Virtual Box could still be the cause, try this: reboot, do not start VBox, give it an hour or so (doing whatever you normally do) and observe the swapfile, then add VBox to the mix and check again.

  • 10. Re: Over 3GB of swap files with 16GB of RAM?
    megagram Level 1 Level 1 (90 points)

    So I loaded up all my big memory users. I upped VBox's VM usage to 2GB to help speed along the process.

     

    I've been checking Activity Monitor regularly and the free mem has not once gone below 8GB (big green part of the pie).

     

    Just now I woke my MacBook from sleep and it hung for about 30 seconds. I checked the /var/vm folder and there are tons of swapfiles that were seemingly just created at that instant.

     

    Wonder what's going on. It's fair to say the last time I used my MacBook there were no swapfiles.

     

    Free memory has always been super high.

    Screen Shot 2012-08-02 at 4.38.17 PM.png

  • 11. Re: Over 3GB of swap files with 16GB of RAM?
    etresoft Level 7 Level 7 (24,270 points)

    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.

  • 12. Re: Over 3GB of swap files with 16GB of RAM?
    David A. Gatwood Level 3 Level 3 (580 points)

    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.

  • 13. Re: Over 3GB of swap files with 16GB of RAM?
    Nathan Goldshlag Level 1 Level 1 (100 points)

    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.

  • 14. Re: Over 3GB of swap files with 16GB of RAM?
    etresoft Level 7 Level 7 (24,270 points)

    Nathan Goldshlag wrote:

     

    Well I *am* seeing a slowdown.

    The cause is not related to virtual memory. The longer you persist in thinking that it is, the longer you will suffer from your slowdown.

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