Memory leak versus inactive memory

Question

Hi:
My iMac was becoming painfully slow a year or so ago. This seemed to be due to a lack of RAM, so I upgraded (2 GB to 4 GB total). This worked great, but now I seem to be running out of memory again, even when there are not a lot of programs open.
I’ve started tracking memory usage with Activity Monitor, and typically a huge chunk of my memory is “Inactive”. I.e., at this time I have 215 MB free, 450 MB Wired, 1.6 GB active, and 1.7 GB inactive. This despite only having Word, Outlook, OmniOutliner, Safari and iTunes open. Under System Memory (in Activity Monitor) it says Finder at 250 MB, Word at 131 MB, iTunes at 120 MB, Outlook at 80 MB, OO at 46 MB, and Dropbox at 34 MB (then a bunch of smaller usages). Even being very generous, the total memory usage only seems to add up to ~1GB, far short of the 4 GB installed.
I have no idea what a real “memory leak” actually is, but I’ve heard the term bandied about. I’ve had some weird, nonreproducible system crashes in the last few months where the system just totally freezes, often (but not always) putting a nice colour pattern on the monitors. Looking around, some folks have said that this might be due to a memory problem since everything else seems to check out AOK.
Thus, several questions:
Might I have a “memory leak”? If so, how do I diagnose and fix it?
What is the 1.7 GB of “inactive” memory being used for? Why is my Free memory so small when this big chunk of inactive memory is sitting there?
Thank you very much!
OS 10.8.2, 2.8 GHz Intel Core 2 Duo with 4 GB 800 MHz DDR2 SDRAM

Answer 1

The way Safari accumulates memory is normal. The way it is trying to page the memory to disc and error-ing is not. I think the integrity of your disc volume / catalog and directories may be to blame.
Try a bit of basic maintenance:
Repairing permissions is important, and should always be carried out both before and after any software installation or update.
Go to Disk Utility (this is in your Utilities Folder in your Application folder) and click on the icon of your hard disk (not the one with all the numbers).
In First Aid, click on Repair Permissions.
This only takes a minute or two in Tiger, but much longer in Leopard.
Background information here:
http://docs.info.apple.com/article.html?artnum=25751
and here:
http://docs.info.apple.com/article.html?artnum=302672
An article on troubleshooting Permissions can be found here:
http://support.apple.com/kb/HT2963
By the way, you can ignore any messages about SUID or ACL file permissions, as explained here:
http://support.apple.com/kb/TS1448?viewlocale=en_US
If you were having any serious problems with your Mac you might as well complete the exercise by repairing your hard disk as well. You cannot do this from the same start-up disk. Reboot from your install disk (holding down the C key). Once it opens, select your language, and then go to Disk Utility from the Utilities menu. Select your hard disk as before and click Repair.
Once that is complete reboot again from your usual start-up disk.
More useful reading here:
Resolve startup issues and perform disk maintenance with Disk Utility and fsck
http://support.apple.com/kb/TS1417?viewlocale=en_US
For a full description of how to resolve Disk, Permission and Cache Corruption, you should read this FAQ from the X Lab:
http://www.thexlab.com/faqs/repairprocess.html