Virtual memory is a critical abstraction in modern computer systems.
Its common model, paging, is currently seeing considerable innovation,
yet its implementations continue to be co-designs between power-hungry/latency-adding
hardware (e.g., TLBs, pagewalk caches, pagewalkers, etc) and software
(the OS kernel). We make a case for a new model for virtual memory,
compiler- and runtime-based address translation (CARAT), which
instead is a co-design between the compiler and the OS kernel. CARAT
can operate without any hardware support, although it could also
be retrofitted into a traditional paging model, and could leverage
simpler hardware support. CARAT uses compile-time transformations and
optimizations combined with tightly-coupled runtime/kernel
interaction to generate programs that run efficiently in a physical
address space, but nonetheless allow the kernel to maintain protection
and dynamically manage physical memory similar to what is possible using
traditional virtual memory. We argue for the feasibility of CARAT
through an empirical study of application characteristics and kernel
behavior, as well as through the design, implementation, and
performance evaluation of a CARAT prototype. Because our prototype
works at the IR level (in particular, via LLVM bitcode), it can be
applied to most C and C++ programs with minimal or no restrictions.