Description:
------------
I've found very strange behavior, which is (unfortunately) consistent across multiple PHP versions: https://3v4l.org/ppe5R

Test script:
---------------
<?php
gc_enable();
echo memory_get_usage(true)/1024 . "\n";

    function callFunc($i = 0) {
        if ($i < 100000) {
           gc_collect_cycles();
           callFunc(++$i);
        }
    }

callFunc();
gc_collect_cycles();
echo memory_get_usage(true)/1024 . "\n";

callFunc();
gc_collect_cycles();
echo memory_get_usage(true)/1024 . "\n";

Expected result:
----------------
Memory should be freed after recursion.

Actual result:
--------------
Memory is retained during lifetime of a recursion, but it's never freed.