Solaris

Oh, I completely agree. But with almost 900MB free physical memory, why is this necessary?

Are you asking why swap is necessary? It is how this system works It needs to be always sure that when available physical memory drops to zero, it will have disk space to send processes and their data to, to free it up. And from your vmstat output it seems that you may have real swap shortage. ~500MB of free swap is really not enough.

No, I completely agree. But why is the system not using any of the remaining physical memory? Also, shouldn't we be seeing scan reads?

I realize that part of physical memory is used for swap and then there is "disk" swap space. I'm just not understanding why our system isn't using the remaining 900MB of physical (or at least 500 of it, with the 500MB remaining swap).

How much free physical memory you have is irrelevant. Free memory is part of virtual memory so is backing reservation too. You are confusing memory reservation and usage.

Well, I didn't hear about using part of physical memory as swap, but main rule I learned while working with SunOS is that there should be always a bit more swap than physical memory available. I don't know exact mechanics behind memory management in Solaris though

That all makes sense, I guess I just would have assumed a vmstat would have shown the system scanning for any unreserved memory to use.

From what I'm seeing, it's like my system has used all the swap it can, all the memory it can and the remaining is reserved. But, at that point I would think it would begin scanning to free memory. That's usually what I would expect.

That depends on what definition of swap you take. When swaps means virtual memory like in the statistics posted, it does. Not necessarily. The rule is there must be enough virtual memory for all reservation to fit. The amount of memory needed is not related to the amount of RAM installed but is related to the number of applications and their requirements.

---------- Post updated at 00:23 ---------- Previous update was at 00:19 ----------

You are confusing physical and virtual memory. The page scanner (if this is what you are referring to) is there to scan used physical memory in case of demand to page it out. This mechanism has no relationship with virtual memory reservations.