MongoDB checks whether THP and THP Defrag are enabled by checking the contents of files present under the '/sys/kernel/mm/transparent_hugepage' directory.

There have been reports that these files can still exist and have the relevant configuration set to 'always' even if THP has been disabled via the boot-time parameter, as described in the preferred method in the online documentation.

Here are some relevant links to RHEL support cases:

1. How to use, monitor, and disable transparent hugepages in Red Hat Enterprise Linux 6? (Note though the test at the end checks for Hugepage support, not Transparent Hugepage support)
2. Disabling transparent hugepages (THP) on Red Hat Enterprise Linux 6 is not taking effect.

Finally, here is what I believe is the reference article for THP support in Linux: Documentation/vm/transhuge.txt