Limiting HHVM memory usage? possible?

i have about 10 sites running off a 1g RAM DO VPS. 7 of them are WordPress. the others just HTML sites running of pagespeed for now. I tried to enable hhvm for a few of the WP sites but the ram usage went up to 80% and the CPU for the www-data user, used by HHVM went up to 98%.

is this normal?

am I doing something wrong?

how do I limit the hhvm memory usage?

what info do you guys need from me to help me?

btw - you guys rock!