memory leak?

[n dhert]

After a reboot of my FreeBSD 8.0-p4 system
a vmstat shows:
Mon Aug 23 08:40:00 CEST 2010
 procs      memory      page                    disks     faults         cpu
 r b w     avm    fre   flt  re  pi  po    fr  sr da0 pa0   in   sy   cs us
sy id
 1 1 0   1515M  7118M   816   5   5   0   726   0   0   0  138 2376 1740  1
2 97
My system had been allocated 8 Gb memory in a Vmware ESXi4 virtual machine.
avm = active virtual pages,  fre = size of free list
2525M + 7118M is 9600M  is this normal? (more than 8 Gb..)

six days ago is was:
Tue Aug 17 14:15:00 CEST 2010
 procs      memory      page                    disks     faults         cpu
 r b w     avm    fre   flt  re  pi  po    fr  sr da0 pa0   in   sy   cs us
sy id
 3 1 0   2446M  1552M   628   0   0   0   621   6   0   0   30  939  572  1
1 98
but before the reboot it was
Mon Aug 23 06:45:00 CEST 2010
 procs      memory      page                    disks     faults         cpu
 r b w     avm    fre   flt  re  pi  po    fr  sr da0 pa0   in   sy   cs us
sy id
 5 22 0   2260M   816M   489   0   0   0   478   2   0   0   27  957  580
1  198
avm + free adds up to only 3 Gb.
Where is the rest of the memory ??

Is there a memory leak, how to find what causes the memory leak?