php中的内存限制问题

 foreach ($saved_test_figurestoprint as $figuretoprint){
        if (strpos($obj[$figuretoprint],\",\") >0 ){
  $graphfilename= \"graphfile\".remove_invalid_chars_for_file($obj[\"_id\"]).\"_\".remove_invalid_chars_for_file($figuretoprint).\".png\" ;        
        $graph = new PHPGraphLib(1000,200,$graphfilename);
        $data = explode(\',\', $obj[$figuretoprint]); 
$graph->addData($data);
$graph->setTitle($figuretoprint);
$graph->setBars(false);
$graph->setLine(true);
$graph->setDataPoints(true);
$graph->setDataPointColor(\'maroon\');
$graph->createGraph();
?> <td> <?  echo $figuretoprint ; ?></td> <td> <? 
echo <<<END
<imag src=$graphfilename>
END

?> </td></tr><tr><?
echo \"</br></br>\";
echo \"used memory is \".memory_get_usage(true) . \"\\n\";