I'm no expert on Parallel::ForkManager, but the module author recommends this code structure:

    use LWP::Simple;
    use Parallel::ForkManager;
 
    ...
 
    @links=(
      ["http://www.foo.bar/rulez.data","rulez_data.txt"],
      ["http://new.host/more_data.doc","more_data.doc"],
      ...
    );
 
    ...
 
    # Max 30 processes for parallel download
    my $pm = new Parallel::ForkManager(30);
 
    foreach my $linkarray (@links) {
      $pm->start and next; # do the fork
 
      my ($link,$fn) = @$linkarray;
      warn "Cannot get $fn from $link"
        if getstore($link,$fn) != RC_OK;
 
      $pm->finish; # do the exit in the child process
    }
    $pm->wait_all_children;
[download]

with the declaration of a new object right before the for loop. Your code has it at the start of your program - perhaps this is causing the extraneous copies.

-Mark