Red Hat first launched Red Hat Enterprise Linux 5 in 2007 and in the latter part of 2010 released Red Hat Linux Enterprise 6, which provided the next generation of enterprise Linux features. Red Hat Enterprise Linux was also recently updated to Red Hat Enterprise Linux 6.2, which gave new control and storage features. The upcoming release of Red Hat Enterprise Linux 5.8, which is now in beta testing, will be getting its own set of updates, though resource control won't be among them.
The resource control functionality found in Red Hat Enterprise Linux 6.2 is from the cgroups feature, which is also not present in the Red Hat Enterprise Linux 5.x series. According to Vice President of Linux Engineering at Red Hat Tim Burke, "cgroups was extremely invasive so you'll never see that in Red Hat Enterprise Linux 5. We continue to do minor feature enhancements in Red Hat Enterprise Linux 5." Burke also added that the minor feature enhancements added to v5 must not be invasive or overly risky and that there is also the potential for additional hardware enablement in Red Hat Enterprise Linux 5.
Even though cgroups isn't going to be in RHEL 5.8, other types of enterprise controls are. Some of the new features support Power Management Quality of Service (QoS), a feature that provides power savings to enterprise via automated scheduling based on QoS policies. In addition to that, there is something known as "iotop" support. This is said to provide monitoring for I/O from a process perspective that will be helpful in troubleshooting performance issues.
According to Burke, "RHEL 5 is still getting development features so it's definitely not the end of the road for RHEL 5. Remember we have a 10-year product lifecycle. At this point RHEL 5 is only four years old, so we still have a long runway left for RHEL 5."
Source: Server Watch - Red Hat Enterprise Linux 5.8 Enters Testing