gistfile1.txt

kronos:rubinius:[master]$ bin/rbx -I heap_dump/lib/ heap_dump/bin/histo.rb heap.dump heap2.dump 
        43                         Method 2408
        40                         String 2880
        40            Rubinius::ByteArray 1600
         3                Rubinius::Tuple 480
         3     Rubinius::GlobalCacheEntry 144
         2          Rubinius::LookupTable 96
         1                          Class 112
         1  Rubinius::LookupTable::Bucket 48
         1          Rubinius::MethodTable 48

Hashes and strings, for example.

Doh! :-)