This code was introduced by bz 18015 https://bugzilla.lustre.org/show_bug.cgi?id=18015
Newer kernels rename that symbol and it's not used anyway, but also at least in RHEL 7. there's bug in this functionality htat leads to use after frees that are seen prominently in our nfs testing in maloo (in addition to my testrig). See LU-11063.
Example nfs failures:
Anyway after reviewing the original patch I think we just need to get rid of this flag altogether and if the rapid load/unload is still a problem, work it around in some better more robust way.