http://php.net/manual/en/book.opcache.php
OPcache improves PHP performance by storing precompiled script bytecode in shared memory, thereby removing the need for PHP to load and parse scripts on each request.
Edit the php configuration file at /etc/php7/apache2/php.ini
To change the value of extension. Then add following lines under [opcache]
opcache.enable=1
opcache.enable_cli=1
opcache.memory_consumption=128
opcache.max_accelerated_files=10000
opcache.interned_strings_buffer=8
opcache.revalidate_freq=60
opcache.fast_shutdown=1
Now restart Apache2 with: sudo service apache2 restart and check in phpinfo.php. We can see all the change.