in Koha/Cache.pm , FastMmap is automatically enable if koha-perldeps are installed, and can't be disable. This feature have to be optionnal because it generate bugs : Open of share file /tmp/sharefile-koha-koha failed: Permission denied at /usr/lib/perl5/Cache/FastMmap.pm line 640.
Running into this again right now...
bug 13431 will fix this problem by making it necessary to turn it on explicitly. *** This bug has been marked as a duplicate of bug 13431 ***