Memory warning hook

As PHP applications are turning into large frameworks one of the issues arriving is memory management. One of the issues is that many frameworks use sophisticated caching techniques to make accessing the same data quickly, this improves speed it is at the cost of memory. Often the developer knows these areas that cache and often times already have functions in place to clear out the cache, however in the case where PHP is approaching or exceeds memory limits PHP runs the GC then dies if it cannot allocate enough memory. If we implemented "memory warning" triggers or user function that will be called before the GC is executed which allows the user to try and free up some memory on their own. This hopefully would give more flexibility to allowing these advanced caching techniques but at the same time allow the cache to be cleared out in case memory is getting low. Thoughts? Thanks, Software Developer Nathan Bruer