I have found, on my machine, that Mac OS X is a little slow to page the right things out.
Whenever doing anything particularly memory hungry, I will often quit a few applications to help it out. Safari is a huge memory hog if it has been running for a while and is top of the list of applications to quit. In my case this was when I tried to run VMWare Fusion without quite enough actual RAM.
You probably know this but here are a couple of links to Apple documentation which describe memory usage and virtual memory on OS X:
http://support.apple.com/kb/ht1342
http://developer.apple.com/library/mac/#documentation/Performance/Conceptual/ManagingMemory/Articles/AboutMemory.html
Here is the explanation that is given: The inactive list contains pages that are currently resident in physical memory but have not been accessed recently. It's hard to get an exact definition of what this means but is seems to include a file system cache as well as actual inactive memory.
Inactive memory is probably a difficult thing to handle on an interactive GUI driven OS where a user may choose to switch to any running application at any time and providing responsiveness in this sort of situation is important.... but the flipside of that is that in a situation like yours the OS doesn't quite know what the right thing to do is.
It is possible to purge (some of) the inactive memory by using the purge command. This may need to be installed by installing the CHUD tools but you may already have that installed. I haven't tried using the purge command so YMMV...
I've rambled on a bit and may or may not have answered your question. After writing all this out, I found another question on this site which much of the same info that might also help.
I was doing some reading about inactive memory after wondering about it myself. My understanding is that inactive memory is memory containing programs and data which you have quit. OS X keeps the memory incase you decide to restart the program. Because it is still in memory it can start it much quicker. You can see this in action by quitting a large program and restarting it. It should start much faster than it originally did.
Inactive memory does not suck up your memory though because OS X regards it as still available for programs to use, jsut at a lower priority than free memory. ie. if OS X needs memory for another program, it will allocate memory from the free area, then the inactive allocation. So when thinking about how much memory you have free for applications to use, inactive and free is combined.
As for swap, if a program is using it you should easily be able to tell by the amount of I/O going on and a noticable slow down.
If you really want to see whats going on I would suggest download iStat menus which is a really nice tool for seeing the internals of your system and display various instruments in the menu bar.
Best Answer
This looks 100% normal, fine and not at all even beginning to look like a problem.
Swap is for items that the system determines aren’t needed actively and frees up RAM for other tasks that can benefit. You have a very large proportion of free memory so the system is well in the green.
Apple’s activity monitor now has a “pressure” gauge so I would look at that and only worry if you see large page in / delays or yellow / red pressure on Apple’s graph.
To check page rates to and from swap, open a shell in terminal.app and run:
You will see counts per minute and the swap in and out are the ones to worry about. Next would be that you have a stable and low amount of free pages so that number going down to 0 or 10 would be worrisome about swap or allocations. Until then, you’re likely at full speed with any amount of swap that’s not filling your drive causing other issues.