### Please describe the problem.

With recent RFing of scanning for unlocked/annexed files (I guess), a sweep of datalad tests on OSX started to take about 3h 30min instead of prior 1h 46min. So pretty much twice. Besides possibly affecting user experience, I am afraid that would cause too much ripples though our CI setup which might not run out of time

Logs etc are at https://github.com/datalad/git-annex/actions/workflows/build-macos.yaml 

The first red is ok, just a fluke but then they all fail due to change in output log string (for which there is a fix but somehow behavior on osx seems different, yet to check).
 



### What version of git-annex are you using? On what operating system?

Currently 8.20210428+git282-gd39dfed2a and first got slow with 
8.20210428+git228-g13a6bfff4 and was ok with 8.20210428+git202-g9a5981a15

[[!meta title="performance edge case when adding large numbers of identical files"]]

> [[fixed|done]] --[[Joey]]
