We are running an integration that requires a webservice with access to the core_course_get_courses function.  Our site has ~8000 courses in the database.  We are receiving the following error.

PHP Fatal error:  Allowed memory size of 2147483648 bytes exhausted (tried to allocate 1052672 bytes) in /var/www/moodle/cache/stores/file/lib.php on line 368" while reading response header from upstream

We have increased the PHP memory to 24GB and still it exhausts the memory.  What can be done?