+ Sort the output (default: 'frag,hit,bytes' for slab and 'bytes,hit'
+ for page). Available sort keys are 'ptr, callsite, bytes, hit,
+ pingpong, frag' for slab and 'page, callsite, bytes, hit, order,
+ migtype, gfp' for page. This option should be preceded by one of the
+ mode selection options - i.e. --slab, --page, --alloc and/or --caller.