Issue: https://github.com/php/php-src/issues/11116
Author: geek-merlin
### Description
Coming from the Drupal world, where a LOT of things are cached in memory. Unfortunately this can
lead to out-of-memory, with no possibility to react.
Were there a low-memory-handler, we could be even more promiscous in caching and still no need to
worry, because a suitably crafted handler will ditch stuff and prevent out-of-memory.