in fact I've installed freememory from the appstore and I can clearly see that my vm use the 4Go alocated to it.
10.8.3 have a bigger footprint than 10.8.2 ... so I'm reaching the limit of my 8Go quickest...
I think it's the explaination ... now can I redust the memory on the footprint off mac osx by turning off some functionalities maybe ...