These do not really exist yet.
These kernels have support for the XFS file system from SGI.

	kernel-2.4.21-40.EL.XFS.athlon.rpm
	kernel-2.4.21-40.EL.XFS.i686.rpm
	kernel-hugemem-2.4.21-40.EL.XFS.i686.rpm
	kernel-smp-2.4.21-40.EL.XFS.athlon.rpm
	kernel-smp-2.4.21-40.EL.XFS.i686.rpm

These contain additional kernel modules.

	kernel-hugemem-unsupported-2.4.21-40.EL.XFS.i686.rpm
	kernel-unsupported-2.4.21-40.EL.XFS.athlon.rpm
	kernel-unsupported-2.4.21-40.EL.XFS.i686.rpm
	kernel-smp-unsupported-2.4.21-40.EL.XFS.athlon.rpm
	kernel-smp-unsupported-2.4.21-40.EL.XFS.i686.rpm

You will also need to install the appropriate kernel-module-xfs-2.4.21-20.0.1.EL

	kernel-module-xfs-2.4.21-40.EL.XFS-1.3.3-1.SL.athlon.rpm
	kernel-module-xfs-2.4.21-40.EL.XFS-1.3.3-1.SL.i686.rpm
	kernel-module-xfs-2.4.21-40.EL.XFSsmp-1.3.3-1.SL.athlon.rpm
	kernel-module-xfs-2.4.21-40.EL.XFSsmp-1.3.3-1.SL.i686.rpm

If you install one of the above kernels and you have openafs then you will
need to update to the appropriate one of these.

	kernel-module-openafs-2.4.21-40.EL.XFS-1.2.11-15.12.SL.athlon.rpm
	kernel-module-openafs-2.4.21-40.EL.XFS-1.2.11-15.12.SL.i686.rpm
	kernel-module-openafs-2.4.21-40.EL.XFSsmp-1.2.11-15.12.SL.athlon.rpm
	kernel-module-openafs-2.4.21-40.EL.XFSsmp-1.2.11-15.12.SL.i686.rpm