Hi all,

I have a question related to single client metadata operations.

While running mdtest benchmark, I have observed that file creation and unlink operations from a single Lustre client quickly saturates to around 8000 iops: maximum is reached as soon as with 4 tasks in parallel.

When using several Lustre mount points on a single client node, the file creation and unlink rate do scale with the number of tasks, up to the 16 cores of my client node.

Looking at the code, it appears that most metadata operations are serialized by a mutex in the MDC layer.

In mdc_reint() routine, request posting is protected by mdc_get_rpc_lock() and mdc_put_rpc_lock(), where the lock is :

struct client_obd -> struct mdc_rpc_lock *cl_rpc_lock -> struct mutex rpcl_mutex.

What is the reason for this serialization ?

Is it a current limitation of MDC layer design ? If yes, are there plans to improve this behavior ?

Thanks,

Grégoire Pichon.