assume the plan is returned by a non-cascading evictor , check whether it is valid . a cascading evictor is an evictor that always tries to move from the target tier to the next tier and recursively move down 1 tier until finally blocks are evicted from the final tier . concode_field_sep PlaceHolder placeHolder concode_field_sep boolean requestSpaceSatisfied concode_elem_sep boolean validCascadingPlan concode_elem_sep boolean blocksInTheSameDir concode_elem_sep void assertEvictionPlanValid