> > Can you replace "_2G" with "_4G" in the decorator for that test?
> 
> When I do that, it pushes the memory usage for the test up to 16GB, which is
> beyond what the machine can handle. When I tried with 2.5G (_2G * 5 // 4),
> that was enough to make it swap heavily (and in the end the test still failed).

Uh, does it? With 4G it should raise OverflowError, and not try to do
anything else.
Could I ask you to try to take a look? :S

> As an aside, it turns out the problem with -M being ignored wasn't due to me
> being stupid; it seems that -j doesn't pass the memlimit on to subprocesses.
> I'll open a separate issue for this.

Running bigmem tests in parallel doesn't make much sense IMO. You want
to run as many of them as you can, which requires that you allocate all
memory to *one* test process.