Over time the GC code has spread out across a number of directories, and currently looks like this:

- There are three "top-level" directories which contain GC-related code:
src/share/vm/gc_interface/
src/share/vm/gc_implementation/
src/share/vm/memory/

- Our collectors are roughly spread out like this:
src/share/vm/gc_implementation/parallelScavenge/ (ParallelGC)
src/share/vm/gc_implementation/g1/ (G1)
src/share/vm/gc_implementation/concurrentMarkSweep/ (CMS)
src/share/vm/gc_implementation/parNew/ (ParNewGC)
src/share/vm/gc_implementation/shared/ (MarkSweep)
src/share/vm/memory/ (DefNew)

- We have common/shared code in the following places:
src/share/vm/gc_interface/ (CollectedHeap, etc)
src/share/vm/gc_implementation/shared/ (counters, utilities, etc)
src/share/vm/memory/ (BarrierSet, GenCollectedHeap, etc)


The plan is for the new structure to look like this:

- A single "top-level" directory for GC code:
src/share/vm/gc/

- One sub-directory per GC:
src/share/vm/gc/cms/
src/share/vm/gc/g1/
src/share/vm/gc/parallel/
src/share/vm/gc/serial/

- A single directory for common/shared GC code:
src/share/gc/shared/