Most of your runtime objects are expected to be pageable in databases designed to support very high storage density because it is necessary as a matter of robus

Most of your runtime objects are expected to be pageable in databases designed to support very high storage density because it is necessary as a matter of robustness and persistability. Even single runtime metadata structures may not reasonably fit in RAM in some cases. There are constraints on these objects (e.g. no vtables) but they are typically not PODs. Even if they were PODs, changing the types and instances of types at a specific memory address without destroying the objects residing there can have side-effects. The compiler does not expect a live memory address to be overwritten with an arbitrary bucket of bits by a DMA operation. DMA doesn't respect lifetime and ownership models as understood by a compiler, so it is a bit of a Deus Ex Machina as far as the compiler is concerned and is assumed to never happen.