Thanks again.
I will debug and post it asap. For now, i turn off XSS setting in mod_security and this VE seem quiet.
HN have Ram 4G and Swap 8G.. but by following vzsplit, it end up with
vmguarpages 0 0 620896 2147483647
That's another question i'd like to ask also. It seem from this point onwards, if i want to increase guarantee ram i have to manually increase pages? bec vzsplit end at 620896 pages which splitting around 16 VEs. If i split 10 VEs only, vmguarpages won't increase anymore than 620896 pages but other parameters such as cpu power increase accordingly.