ZEND_MM_OVERHEAD   38 Zend/zend_gc.c 	((4096 - ZEND_MM_OVERHEAD - sizeof(void*) * 2) / sizeof(gc_root_buffer))
ZEND_MM_OVERHEAD   22 Zend/zend_smart_str.c #define SMART_STR_OVERHEAD (ZEND_MM_OVERHEAD + _ZSTR_HEADER_SIZE)