nofib is incredibly greedy on disk space

I keep running out of disk space, and it turns out to be the nofib build trees. Here is a listing

simonpj@LHR-WD-22561:~/code$ du -d 1 -h HEAD | sort -h -r
16G	HEAD
6.4G	HEAD/nofib
5.0G	HEAD/_build
3.6G	HEAD/.git
274M	HEAD/testsuite
167M	HEAD/libraries
47M	HEAD/hadrian
38M	HEAD/bootstrapping
32M	HEAD/utils
27M	HEAD/compiler
22M	HEAD/inplace
5.1M	HEAD/docs
4.7M	HEAD/rts
2.5M	HEAD/autom4te.cache
1.3M	HEAD/libffi-tarballs
572K	HEAD/ghc
356K	HEAD/m4
256K	HEAD/.gitlab
172K	HEAD/mk
128K	HEAD/linters
116K	HEAD/driver
96K	HEAD/distrib
24K	HEAD/bindisttest
12K	HEAD/libffi

Now it turns out that each nofib run takes another 4G. Compared with 5G for an entire GHC build, that seems like a lot.

If I do a daily nofib run in 4 build trees, that eats up 16G/day, and it's not long before I run out.

After I've run nofib, all I want are the results in run.results.tsv. Maybe a log file. The rest is just a waste of space.

Could we be more parsimonious somehow?