The Red Hat Enterprise Linux v. 3 Kernel: A Linux 2.4 core with Linux 2.6 features

To provide the best possible mix of technology and stability in late 2003, Red Hat Enterprise Linux v.3 implemented a hybrid kernel approach: Features from the Linux 2.6 kernel that would be of most value to commercial/enterprise customers and ISVs were backported for incorporation into the most stable Linux 2.4 kernel. As a result of this approach, the kernel provided a combination of stability, performance, and scalability.

The following table outlines the most important of these kernel features, and notes which ones are included in Linux 2.6 and the Red Hat Enterprise Linux v.3 product family. In general, features that were not backported were, at the time, insufficiently mature for commercial environments, or are not considered necessary by customers and ISV partners. In early 2005 Red Hat Enterprise Linux v.4 was released, which provides a full Linux 2.6 kernel.

Feature In Linux 2.6 kernel In Red Hat Enterprise Linux 3 Provides:
Native Posix Thread Library (NPTL)
Yes
Yes
High performance POSIX compliant multi-threading
Kernel IPSec
Yes
Yes
IPSec layer available for use by kernel modules
Asynchronous I/O (AIO)
Yes
Yes
Improved application performance
O(1) Scheduler
Yes
Yes
Highly scalable SMP scheduler
OProfile
Yes
Yes
CPU-hardware-based performance monitoring
kksymoops
Yes
Yes
Improved kernel bug reporting
Reverse Map Virtual Memory (rmap VM)
Yes
Yes
Performance improvement in memory constrained systems
HugeTLBFS
Yes
Yes
Performance improvement for large virtual memory applications (e.g. Databases)
Remap_file_pages
Yes
Yes
Kernel memory optimization for shared memory applications
2.6 Network stack features (IGMPv3, Ipv6, etc.)
Yes
Yes
Improved network performance & messaging
IPvs
Yes
Yes
Network load balancing
Access Control Lists (ACLs)
Yes
Yes
Improved file system security management
4GB-4GB memory split
No
Yes
Greatly increased x86 physical memory support and larger application address space
Scheduler support for hyperthreaded CPUs
No
Yes
Improved hyperthreaded CPU performance. (2.6 implementation not yet comparable)
Block I/O (BIO) block layer
Yes
No
Major rewrite of the I/O subsystem (stabilization and driver support in progress)
Support for > 2TB file system
Yes
No
Support for very large volumes. Red HatEnterprise Linux 3 supports up to 2TB.
New I/O elevators
Yes
No
Fine tuning for I/O subsystem performance (stabilization in progress)
Interactive scheduler response tuning
Yes
No
Scheduler improvements for interactive tasks (stabilization in progress)