On Mon, 2011-10-31 at 14:31 -0400, Jim Rees wrote: > Trond Myklebust wrote: > > I don't necessarily disagree with what you are saying, but I have yet to > see a single server side implementation of CB_RECALL_ANY, let alone any > numbers that indicate performance or responsiveness problems resulting > from our existing client-side implementation. > > I therefore find it hard to understand why optimising this particular > code is such a high priority, or why a patch that is adding per-file > layoutreturns to initiate_bulk_draining() is going to help anything at > all. > > Testing between the linux block layout client and the EMC block layout > server revealed a deadlock when the server had handed out some number of > layouts and couldn't hand out any more. So now the EMC block layout server > implements CB_RECALL_ANY. So yes, this solves a real world problem, and > yes, there is a server that implements this. > > We had some discussions at the time, and I don't remember if those were on > the linux-nfs list or in some other forum. We decided that the client was > in the best position to decide which layouts were no longer needed, so we > needed some way for the server to tell the client to return some layouts > without specifying which ones. CB_RECALL_ANY seemed custom-made for this > purpose, so we used it. > > I don't think it would be appropriate for the server to recall all layouts > when it only needs some of them back. As I said previously: the current client implementation deals with CB_RECALL_ANY by calling initiate_file_draining(), which forgets _all_ layouts. If that is what we want to continue to use, then sending layoutreturn with LAYOUTRETURN4_ALL is appropriate. Otherwise, please fix the client to be more selective (in which case LAYOUTRETURN4_FILE may be more appropriate) and please remember to provide performance numbers to justify the need for optimisation. -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@xxxxxxxxxx www.netapp.com -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
