func (p *Process) allocHeapInfo(a core.Address) *heapInfo {
	k := a / heapInfoSize / pageTableSize
	i := a / heapInfoSize % pageTableSize
	t := p.pageTable[k]
	if t == nil {
		t = new(pageTableEntry)
		for j := 0; j < pageTableSize; j++ {
			t[j].firstIdx = -1
		}
		p.pageTable[k] = t
		p.pages = append(p.pages, k)
	}
	return &t[i]
}
func (p *Process) allocHeapInfo(a core.Address) *heapInfo {
	k := a / heapInfoSize / pageTableSize
	i := a / heapInfoSize % pageTableSize
	t := p.pageTable[k]
	if t == nil {
		t = new(pageTableEntry)
		for j := 0; j < pageTableSize; j++ {
			t[j].firstIdx = -1
		}
		p.pageTable[k] = t
		p.pages = append(p.pages, k)
	}
	return &t[i]
}
// Same as findHeapInfo, but allocates the heapInfo if it
// hasn't been allocated yet.