This functionality appears to have been introduced in linux 2.6.33 with commit a2e272554 . Looking at http://vault.centos.org/6.8/updates/Source/SPackages/kern

This functionality appears to have been introduced in linux 2.6.33 with commit a2e272554 . Looking at http://vault.centos.org/6.8/updates/Source/SPackages/kernel-2.6.32-642.4.2.el6.src.rpm http://vault.centos.org/6.8/updates/Source/SPackages/kernel-... it looks like RedHat backported this function but has not applied the fix.