I've also added some restrictions for apache which seems not to change the problem :
<IfModule prefork.c> MaxClients 40 MaxSpareServers 8 MaxRequestsPerChild 2000 </IfModule>
RLimitNPROC 10 RLimitMEM 67108864 RLimitCPU 30
I've also added some restrictions for apache which seems not to change the problem :
<IfModule prefork.c>
MaxSpareServer s 8
MaxRequestsPer Child 2000
MaxClients 40
</IfModule>
RLimitNPROC 10
RLimitMEM 67108864
RLimitCPU 30