Symbolism, Imagery, Allegory
Lin only remembers the Australian prison he escaped from in flashbacks, and none of those memories have anything remotely positive attached to them. The prison in Shantaram represents the past. It's what Lin is running away from, everything he doesn't want to remember.
He might have been tortured by prison guards and fellow prisoners, but now Lin is tortured by thoughts of his crimes. He remembers "the torment of what I'd done, and what I'd become—the pain and the fear and the waste; the stupid, unforgiveable waste of it all" (1.5.287). Just like that prison that tried to hold him, Lin attempts to escape from his own guilty conscience.
Lin's plan for escape from the prison is what he calls "heroic if it succeeds, and insane if it fails" (2.9.2). He has to find the same kind of heroism to escape from his past; his fingerprints try to give him away, and he has to change his name and erase every scrap of identifying information to leave the walls and memories behind.