Admonished to get everything updated, I turned to my raspberry pi with
Sakaki's binary image.  Synced and updated portage with no problem. 
Then I did an emerge -u @world and got (after *hours* of dependency
checking):

 >>> Jobs: 0 of 206 complete, 1 running Load avg: 2.84, 3.44, 3.85
 >>> Emerging binary (1 of 206) sys-libs/glibc-2.31-r5::gentoo
 >>> Jobs: 0 of 206 complete, 1 running Load avg: 2.84, 3.44, 3.85
 >>> Jobs: 0 of 206 complete Load avg: 3.60, 3.54, 3.87
 >>> Installing (1 of 206) sys-libs/glibc-2.31-r5::gentoo
 >>> Jobs: 0 of 206 complete Load avg: 3.60, 3.54, 3.87
Exception in callback AsynchronousTask._exit_listener_cb(<bound
method...0x7f9180d9d8>>)
handle: <Handle AsynchronousTask._exit_listener_cb(<bound
method...0x7f9180d9d8>>)>
Traceback (most recent call last):
   File "/usr/lib64/python3.6/asyncio/events.py", line 145, in _run
     self._callback(*self._args)
   File
"/usr/lib64/python3.6/site-packages/_emerge/AsynchronousTask.py", line
201, in _exit_listener_cb
     listener(self)
   File
"/usr/lib64/python3.6/site-packages/_emerge/BinpkgPrefetcher.py", line
31, in _fetcher_exit
     self._start_task(verifier, self._verifier_exit)
   File "/usr/lib64/python3.6/site-packages/_emerge/CompositeTask.py",
line 113, in _start_task
     task.start()
   File
"/usr/lib64/python3.6/site-packages/_emerge/AsynchronousTask.py", line
30, in start
     self._start()
   File "/usr/lib64/python3.6/site-packages/_emerge/BinpkgVerifier.py",
line 59, in _start
     self._digester_exit)
   File "/usr/lib64/python3.6/site-packages/_emerge/CompositeTask.py",
line 113, in _start_task
     task.start()
   File
"/usr/lib64/python3.6/site-packages/_emerge/AsynchronousTask.py", line
30, in start
     self._start()
   File
"/usr/lib64/python3.6/site-packages/portage/util/_async/FileDigester.py",
line 30, in _start
     ForkProcess._start(self)
   File "/usr/lib64/python3.6/site-packages/_emerge/SpawnProcess.py",
line 112, in _start
     retval = self._spawn(self.args, **kwargs)
   File
"/usr/lib64/python3.6/site-packages/portage/util/_async/ForkProcess.py",
line 24, in _spawn
     pid = os.fork()
   File "/usr/lib64/python3.6/site-packages/portage/__init__.py", line
246, in __call__
     rval = self._func(*wrapped_args, **wrapped_kwargs)
OSError: [Errno 12] Cannot allocate memory

What's the recommended course of action here?

Log attached.