php gzip xml文件(53MB)出现内存不足错误

我有一个53mb的xml文件,我想要gzip。

下面的代码是gzip-it

$gzFile = "my.gz";

        $data = IMPLODE("", FILE($filename)); 
        $gzdata = GZENCODE($data, 9); 

        //open gz -- 'w9' is highest compression
        $fp = gzopen ($gzFile, 'w9');       
        //loop through array and write each line into the compressed file       
        gzwrite ($fp, $gzdata);

        //close the file
        gzclose ($fp);

这个原因

PHP Fatal error:  Out of memory (allocated 70516736) (tried to allocate 24 bytes) 

任何人都有什么建议。

我已经在php.in I中增加了内存