fork()ing will not release memory, yes. But think about this:

@ARGV = ('--restart', Data::Dumper::Dumper(\%whatever));
exec( $^X, $0, @ARGV );
RESUME: #only if you really need to!
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and at the beginning of your program:

if ($ARV[0] eq '--restart') {
  %whatever = %{ eval $ARGV[1] };
  goto RESUME; #only if you really need to!
}
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Or you can use a temporary file to store your variables. There is not that much space in @ARGV...