multiple image upload eats much space on the RAM - php

Question

I added multiple file upload on my website, but I noticed, that uploaded files eat much RAM on the server and it does not decrease for 1-2 days. I think the reason is incorrect PHP code... I tried to unset all variables but it didn't help. That's my code:
<?php
if(isset($_POST['upload'])){
if(count($_FILES['files']['name']) > 0){
for($i=0; $i<count($_FILES['files']['name']); $i++) {
$tmpFilePath = $_FILES['files']['tmp_name'][$i];
if($tmpFilePath != ""){
$max_filesize = 10000288;
if(filesize($_FILES['files']['tmp_name'][$i]) > $max_filesize)
die('File is too large.');
if($_FILES['files']['type'][$i] != "image/jpeg" AND $_FILES['files']['type'][$i] != "image/png")
die('This is not available format.');
$shortname = $_FILES['files']['name'][$i];
$filePath = "img/uploaded_images/full/" .date('d-m-Y-H-i-s').'-'.$_FILES['files']['name'][$i];
if(move_uploaded_file($tmpFilePath, $filePath)) {
$files[] = $shortname;
$tmpFilePath = NULL;
$allowed_filetypes = NULL;
$max_filesize = NULL;
$filePath = NULL;
$_FILES['files']['name'][$i] = NULL;
$shortname = NULL;
$_FILES['files']['tmp_name'][$i] = NULL;
unset( $tmpFilePath);
unset($allowed_filetypes);
unset($max_filesize);
unset($filePath);
unlink($_FILES['files']['name'][$i]);
unset($_FILES['files']['name'][$i]);
unset($shortname);
unset($_FILES['files']['tmp_name'][$i]);
}
}
}
$_FILES = NULL;
unset($_FILES);
}
} ?>