Php memory leak

<?php

// some sort of hack to get httpd.exe size in mb
function httpd_mb()
{
    //"httpd.exe","10744","Services","0","112 924 Kb"
    $cmd = 'tasklist /fi "imagename eq httpd.exe" /fo csv /nh'; // no header
    $res = exec($cmd, $lines);
    $kbs = explode(',',$lines[1])[4];
    $kb = preg_replace('/[^0-9]/','',$kbs);
    $mb = round($kb/1024);
    return $mb;
}

function info()
{
    global $data, $chunk_size_kb;
    $c = count($data);
    $httpd_mb = httpd_mb();
    echo 'apache size: ' . $httpd_mb . ' mb, ';
    echo 'memory usage/real usage: ' . round(memory_get_usage()/1024/1024);
    echo '/' . round(memory_get_usage(true)/1024/1024) . ' mb (';
    echo $c . ' items in array, ';
    echo round($chunk_size_kb*$c/1024) . ' mb stored)';
    echo '<br>';
    flush();
    return $httpd_mb;
}

function shutdown()
{
    echo '<br><b>before crash</b>:<br>';
    info();
}


// SETTINGS SECTION (feel free to experiment with it)

ini_set('memory_limit', '1500M'); // memory leaks faster then limit is bigger.
$chunk_size_kb = 2043; // on my system 2043kb leaks, 2044 frees memory, everything is ok
$stat_freq = round(100000 / $chunk_size_kb);

// END OF SETTINGS




register_shutdown_function('shutdown');
$data = array();
$ap = info();

// if memory already busy (httpd >> 1G), run this block and fail to alloc memory
$big_chunk_mb = 200;
if ($ap > 1800-$big_chunk_mb)
{
    echo "<h3>apache overloaded ($ap mb), trying to alloc $big_chunk_mb mb</h3>";
    $big = str_repeat('1',$big_chunk_mb*1024*1024);
}

// main cycle, allocates memory to array of relatively small strings (<2mb)
for ($i=0; true; $i++)
{
    //$data[] = random_bytes($chunk_size_kb*1024); // the same result
    $data[] = str_repeat('1',$chunk_size_kb*1024);

    if ($i % $stat_freq == $stat_freq-1)
        info();

    // looks like any fatal error also keeps memory
    //if ($i == 2000)
    //  trigger_error('stop', E_USER_ERROR);
}

?>