Memory used by unknown processes

Question

Hey all,
I have a serious problem on my 2008 model macbook running snow leopard 10.6.8 with 4GB of memory
Used memory continuosly grows even though no work is being done (i.e. no application opened).
It gets to a point where free memory goes almost to zero and only then system apparently frees some of it.
Using free memory app I can free memory manually but still after freeing, free memory continue to decline.
What really bothers me is that the sum of all memory used by processes (from both activity monitor and ps command) does not sum up to total used memory.
Can some "invisible" process be using my memory? or ps/activity monitor outputs are not correct?

Answer 1

Not exactly sure what you mean.
Here's output from top (the header):
Processes: 74 total, 3 running, 1 stuck, 70 sleeping, 535 threads                                                        13:40:42
Load Avg: 0.36, 0.22, 0.35  CPU usage: 8.33% user, 41.66% sys, 50.0% idle    SharedLibs: 5888K resident, 8800K data, 0B linkedit.
MemRegions: 13884 total, 1746M resident, 28M private, 380M shared.
PhysMem: 590M wired, 2219M active, 1025M inactive, 3834M used, 261M free.
VM: 178G vsize, 1043M framework vsize, 738071(0) pageins, 235(0) pageouts. Networks: packets: 660846/677M in, 332007/37M out.
Disks: 327320/5791M read, 154559/5840M written.
And here's the sum of RSS from ps:
# ps -axm -o "rss,comm"|grep -v COMM|awk 'BEGIN{a=0}{a+=$1}END{print a}'
2537976
As you can see, top reports 3834MB as used, while sum of RSS from ps shows ~2.5GB