This wiki article contains incomplete and informal notes about the MPS, the precursor to more formal documentation. Not confidential. Readership: MPS users and developers.

Scope of terms

Terms are marked as being applicable in the following scopes:

(general)
term in general use in the memory-management community; see The Memory Management Glossary.
(mps.h)
term used in the published MPS interface or published documentation, for client programs to use
(internal)
term used in internal MPS code or design documentation (not for use in client programs)

Note: often an mps.h term has a related (but not exactly corresponding) internal term. The distinction can be critical.

Terms

Client ≈ Mutator:

Client (mps.h)
The program that uses the MPS via the mps.h interface.
Mutator (internal)
The computational process that mutates (edits) the graph of references

Allocation Point ≈ Buffer:

Allocation Point (mps.h)
MPS protocol that client uses to allocate memory with low overhead, and low thread-synchronization cost.
Buffer (internal)
A piece of memory held by the MPS, often used to provide memory for an allocation point.

Pieces of memory

Pools getting raw memory from the Arena

This memory will be used for client objects. There are two interfaces: a high-level "segment" interface, and a simpler "arena memory" interface.

segment (internal)

= a contiguous piece of memory of arbitrary size, with associated properties for participating in garbage collection (see SegStruct).

A pool may call SegAlloc() to request a segment from the arena. The segment is the unit of pool-to-pool and pool-to-MPM interaction for GC.

Design: design/seg.

Interface: SegAlloc() et al in mpm.h.

Historical note: before 'sunset on segments' (1999-11-18, change 21000) a segment was a VM page.

arena memory (internal)

= a contiguous piece of memory of arbitrary size, returned by ArenaAlloc()

A pool may call ArenaAlloc() to request raw memory from the arena. This is a simpler interface than segments, suitable for simple pools that do not participate in garbage collection, pools used internally by the MPM, etc.

(Note: this ArenaAlloc() interface is sometimes called the "tract" interface).

Pools getting memory for administrative use

This memory will be used for the pool's administrative datastructures, such as allocation tables.

control memory (internal)

Pools use ControlAlloc() and ControlFree() to obtain or free control memory.

How the arena handles memory

See tract.c.

chunk (internal)

= a contiguous (I think) piece of address space that has been reserved (I think) by the arena

arena->primary points to the arena's first chunk

page (internal)
= unit of granularity of arena allocation; object corresponding to one operating-system VM page
tract (internal)
= a page that is allocated to a pool

Other terms:

foreign code (mps.h)
From the MPS client's point of view, foreign code is external code (outside the client and MPS), which is not aware of and does not cooperate with the MPS. Examples include the operating system, graphics libraries, etc. Before the client passes MPS memory references to foreign code, it must ensure that the memory is not going to be moved, collected, or protected by the MPS. Some pool classes (eg. mps_class_lo ) are specially designed for this.
format (mps.h)
A collection of client-implemented Format Methods, which MPS uses to ask the client questions about objects. See GC.
Attr (internal)
A bitset of pool or pool class attributes. See design/type/#attr.
Ring (internal)
A Parent node, linked to zero or more Child nodes. Used throughout MPS internals. See design/ring. The RING_FOR macro visits all Child nodes. Note: when a node (RingStruct) appears in a larger structure, there is (alas) no indication whether it is the parent node, or a child node.

B. Document History

  2006-06-06  RHSK  Created.
  2006-06-21  RHSK  Scope of terms; client/mutator, ap/buffer.
  2006-07-03  RHSK  Ring.
  2006-08-02  RHSK  Foreign code.  Format (clarify).
  2006-08-14  RHSK  Pieces of memory: chunk, segment, tract, page

C. Copyright and License

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