In bpo-26588, I modified the _tracemalloc module to support tracing memory allocations in multiple "domains" for numpy. I modified hashtable.c to support keys larger than void*, and I modified _tracemalloc.c to use a new pointer_t structure which is made of (domain: unsigned int, ptr: void*).

These changes made hashtable.c way more complicated than what it should be. I would like to reuse hashtable.c in more places. I am working on a change to remove the pointer_t type from _tracemalloc.c, and instead use a hash table for traces of domains other than the default domain (0). The new hash table maps a domain to a hash table: traces of a domain.

tracemalloc_traces remains the default hash table for traces of the default domain. Since it's the most common case, it doesn't go through the new hash table.

New changeset 9e2ca1742076169089b818d0883688a2ddd9964a by Victor Stinner in branch 'master':
bpo-40609: Rewrite how _tracemalloc handles domains (GH-20059)
https://github.com/python/cpython/commit/9e2ca1742076169089b818d0883688a2ddd9964a

New changeset f9b3b582b86b9cce8d69ec7d03d716ec81c8264a by Victor Stinner in branch 'master':
bpo-40609: Remove _Py_hashtable_t.key_size (GH-20060)
https://github.com/python/cpython/commit/f9b3b582b86b9cce8d69ec7d03d716ec81c8264a

New changeset 2d0a3d682f699cce8db6e30981d41d9125318726 by Victor Stinner in branch 'master':
bpo-40609: Add destroy functions to _Py_hashtable (GH-20062)
https://github.com/python/cpython/commit/2d0a3d682f699cce8db6e30981d41d9125318726

New changeset d95bd4214c2babe851b02562d973d60c02e639b7 by Victor Stinner in branch 'master':
bpo-40609: _tracemalloc allocates traces (GH-20064)
https://github.com/python/cpython/commit/d95bd4214c2babe851b02562d973d60c02e639b7

New changeset 5b0a30354d8a8bb39a05ce10ca4f5c78b729f25b by Victor Stinner in branch 'master':
bpo-40609: _Py_hashtable_t values become void* (GH-20065)
https://github.com/python/cpython/commit/5b0a30354d8a8bb39a05ce10ca4f5c78b729f25b

I modified _Py_hashtable_t to remove key_size and data_size: keys are now always "void *" and values are now always "void *".

See also bpo-40602: Move Modules/hashtable.h to Include/internal/pycore_hashtable.h.