question: public void unmap ( int addr , int len ) { for ( int i = 0 ; i < len ; i += PAGE_SIZE ) { int pte = getPTE ( addr + i ) ; if ( getPage ( pte ) != null ) { readableMemory [ pte ] = null ; writableMemory [ pte ] = null ; executableMemory [ pte ] = null ; } else { throw new Error ( "Unmapping memory that's not mapped addr=0x" + Integer . toHexString ( addr ) + " len=" + len ) ; } } }
target:  Unmap a page of memory