Scheduler cells are small objects that come and go in great quantities.
Even though they are allocated and deallocated a lot, they tend to a
steady state quantity, so put together a heap that is unique for each
cell type.
This heap actually saves memory overall because cells are allocated in
chunks, thus eliminating allocator overhead, and they are pulled/pushed
from/to a heap very quickly so that what overhead remains is slight and
bounded.
Stephen Williams