PHP upload does not get the file information

I use Ajax to upload files to PHP in the php file size to run the scope of all the files can be obtained, but I uploaded a file if it is 300M PHP there will not get anything to print the return information is as follows:
Array (0) {}
No Properties

How can I get the file information or how to determine the file size without changing the upload size of various configuration files such as PHP and browsers? Because the file here is not to get anything more than to judge the size of the file, but also please the Great God guidance!

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