The memory usage at mount time for lustre 2.1 appears to be significantly worse than under 1.8. In particular, it looks like slab-8192 usage has grown significantly.

On 1.8 clients, the memory usage by lustre is maybe 1GB of memory to mount four of our filesystems.

On 2.1 clients, the memory usage has jumped to 5GB of memory to mount the same four filesystems.

It looks like there are 3144 oscs at this time.

The memory pretty clearly increases with each filesystem mounted, and then reduces again at each umount. I would suspect that we have some bad new per-osc memory usage or something along those lines, or otherwise there would be more fallout.

But this is a pretty significant loss of memory, and it means that our applications are now OOMing on the 2.1 clients. Many of the applications are very specifically tuned in their memory usage, and the loss 4GB of memory per node is quite a problem.