[Lustre-devel] Queries regarding LDLM_ENQUEUE

Nicolas Williams Nicolas.Williams at oracle.com
Wed Oct 20 07:55:57 PDT 2010


On Wed, Oct 20, 2010 at 10:51:06AM -0400, Paul Nowoczynski wrote:
> Eric makes a good point in that only parallel jobs really need this 
> feature. Unfortunately, at scale the system (both clients and servers) 
> *really do* need something like this, especially if we continue pushing 
> users to perform N-1 file I/O instead of 'file per process'. I too am in 
> agreement that some sort of capability mechanism is the best approach. I 
> wonder if this is something that could be done outside of POSIX and 
> supported through a parallel I/O library? Perhaps a single application 
> threads could make a special open call (/proc magic perhaps?) and obtain 
> the glob of opaque bytes which are then broadcast to the rest of the 
> client via mpi. Traversing the namespace would be avoided on all but one 
> client. In such a scenario I don't feel that enforcing unix permissions 
> at every level of the path is needed or sensible, the operation should 
> be treated as a simple logical open. The question to the lustre experts 
> - can enough state be packed into an opaque object such that the 
> recv'ing client can construct the necessary cache state?

POSIX already has what you're asking for, and it's called openg() ;)



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