If i'm not mistaken, the 'read barrier' is only active during a mark of the heap, not all the time. So, considering that marking can be parallelized and there'

If i'm not mistaken, the 'read barrier' is only active during a mark of the heap, not all the time. So, considering that marking can be parallelized and there's a good chance a lot of the heap is now dead objects (you only mark live ones) you shouldn't be too affected.