DOCSP-3838 clarify tuned recommendation in production checklist

source/administration/production-checklist-operations.txt

@@ -203,13 +203,16 @@ Linux
        an optimal value that maximizes the resident memory and lowers the
        number of page faults.
 
-   - Disable the ``tuned`` tool if you are running RHEL 7 / CentOS 7 in a
-     virtual environment.
-
-     When RHEL 7 / CentOS 7 run in a virtual environment, the ``tuned`` tool
-     automatically invokes a performance profile derived from
-     performance throughput, which automatically sets the readahead
-     settings to 4MB. This can negatively impact performance.
+   - If using ``tuned`` on RHEL / CentOS, you must customize your
+     ``tuned`` profile. Many of the ``tuned`` profiles that ship with
+     RHEL / CentOS can negatively impact performance with their default
+     settings. Customize your chosen ``tuned`` profile to:
+
+     - Disable transparent hugepages. See
+       :ref:`Using tuned and ktune <configure-thp-tuned>` for
+       instructions.
+     - Set readahead between 8 and 32 regardless of storage media type.
+       See :ref:`Readahead settings <readahead>` for more information.
 
    - Use the ``noop`` or ``deadline`` disk schedulers for SSD drives.