This bug has been copied from bug #636198 and has been proposed to be backported to 5.5 z-stream (EUS).
in kernel-2.6.18-194.26.1.el5 linux-2.6-net-mlx4-bump-max-log_mtts_per_seg-memory-reservation.patch
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on therefore solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2010-0839.html
Technical note added. If any revisions are required, please edit the "Technical Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: With this update, the upper limit of log_mtts_per_seg was increased from 5 to 7, increasing the amount of memory that can be registered. Machines with larger memory are now able to register more memory.