message: doc: more definitions
diff: @@ -12,8 +12,24 @@ for details.
  The entry point of the library is [`libmesh.cc`](src/libmesh.cc).
  This file is where `malloc`, `free` and the instantiations of the
  -Heaps used for allocating program and mesh-internal memory live.
  -
  +Heap used for allocating program memory lives.
  +
  +
  +DEFINITIONS
  +-----------
  +
  +- **Page**: The smallest block of memory managed by the operating system,
  + 4Kb on Linux. Memory given to the allocator by the operating system
  + is always in multiples of the page size, and aligned to the page
  + size.
  +- **Span**: The size of memory managed by Mesh -- [currently 128
  + Kb](src/include/miniheap.h#L36).
  + It is larger than the page size to amortize the cost of heap
  + metadata.
  +- [**MiniHeap**](src/include/miniheap.h): A bitmap, metadata and associated Span for a
  + particular size of objects (size class).
  +- [**MeshingHeap**](src/include/meshingheap.h): A collection of miniheaps for a particular size
  + class, including a _current_ MiniHeap that we are allocating out of.
  BUILDING
  --------
  