[Lustre-discuss] Shared pointers, file locking and MPI-IO

Sébastien Buisson sebastien.buisson at bull.net
Thu Oct 23 07:06:33 PDT 2008

Hi all,

We are using MPI-IO on Lustre, so that we can achieve good performance 
when writing or reading the same file from multiple processes and clients.
In the shared pointers read/write routines, MPI-IO makes an intensive 
use of file locks (for instance, see the file 
src/mpi/romio/adio/common/ad_get_sh_fp.c from mpich2-1.0.7). The problem 
is that file locking support in Lustre is very limited today:
- there is the localflock option for the local mode. In this mode, locks 
are coherent on a node (a single-node flock), but not across all clients;
- there is the flock option for the consistent mode. In this mode, locks 
are coherent across all clients. But the Lustre Operations Manual 
includes a big warning about this mode, saying that it can affect 
performance and stability.

That being said, does anybody in the Lustre community know about current 
alternatives to the MPI-IO shared pointers read/write routines, which do 
not use the file locking mechanism but provide the same functionality?

By the way, do we have an idea of the Lustre version that will provide 
the reliable version of the flock consistent mode?

Best regards,

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