A Caching Model of Operating System Kernel Functionality
--- Duda et al., 1994


- Main idea: define the concept of a caching model of operating system
  functionality.  The idea is to cache the currently used objects, leaving
  the possibility of implementing application-specific management 
  policies and mechanisms in application kernels running in user-mode.

- micro-kernels have been slower, larger and more error-prone than
  desired;

- they are larger because of the complications of a modern virtual memory 
  system, the need to support many different hardware devices, and
  complex optimizations in communication facilities.

- micro-kernels do not support domain-specific resource allocation
  policies any better than monolithic kernels;

- adding a variety of resource management policies to the micro-kernel
  fails to achieve the efficiency that application-specific knowledge
  allows and increases the kernel size and complexity;

- the Cache kernel caches active objects: address spaces, threads,
  scheduling and IPC.

- in contrast to conventional micro-kernel design, it does not fully
  implement all the functionality associated with address spaces and
  threads;

- it relies on higher-level application kernels to provide the
  management functions required for a complete implementation,
  including the loading and write-back of these objects.

- application kernels control physical page selection, page
  replacement policy and paging I/O;

- applications run above application kernels, which run on top of the
  supervisor-mode Cache kernel.

- interactions between application kernels and Cache kernel occur to
  load/unload these objects, signals from the Cache kernel about
  missing objects, and write-back communication (object is evicted);