On Thu, Apr 25, 2013 at 02:51:20PM -0400, Chuck Lever wrote: > > On Apr 25, 2013, at 2:46 PM, "bfields@xxxxxxxxxxxx" <bfields@xxxxxxxxxxxx> wrote: > > > On Thu, Apr 25, 2013 at 02:40:11PM -0400, Chuck Lever wrote: > >> > >> On Apr 25, 2013, at 2:19 PM, "bfields@xxxxxxxxxxxx" <bfields@xxxxxxxxxxxx> wrote: > >> > >>> On Thu, Apr 25, 2013 at 02:10:36PM +0000, Myklebust, Trond wrote: > >>>> On Thu, 2013-04-25 at 09:49 -0400, bfields@xxxxxxxxxxxx wrote: > >>>>> On Thu, Apr 25, 2013 at 01:30:58PM +0000, Myklebust, Trond wrote: > >>>>>> On Thu, 2013-04-25 at 09:29 -0400, bfields@xxxxxxxxxxxx wrote: > >>>>>> > >>>>>>> My position is that we simply have no idea what order of magnitude even > >>>>>>> delay should be. And that in such a situation exponential backoff such > >>>>>>> as implemented in the synchronous case seems the reasonable default as > >>>>>>> it guarantees at worst doubling the delay while still bounding the > >>>>>>> long-term average frequency of retries. > >>>>>> > >>>>>> So we start with a 15 second delay, and then go to 60 seconds? > >>>>> > >>>>> I agree that a server should normally be doing the wait on its own if > >>>>> the wait would be on the order of an rpc round trip. > >>>>> > >>>>> So I'd be inclined to start with a delay that was an order of magnitude > >>>>> or two more than a round trip. > >>>>> > >>>>> And I'd expect NFS isn't common on networks with 1-second latencies. > >>>>> > >>>>> So the 1/10 second we're using in the synchronous case sounds closer to > >>>>> the right ballpark to me. > >>>> > >>>> OK, then. Now all I need is actual motivation for changing the existing > >>>> code other than handwaving arguments about "polling is better than flat > >>>> waits". > >>>> What actual use cases are impacting us now, other than the AIX design > >>>> decision to force CLOSE to retry at least once before succeeding? > >>> > >>> Nah, I've got nothing, and I agree that the AIX problem is there bug. > >>> > >>> Just for fun I looked at re-checked the Linux server cases. As far as I > >>> can tell they are: > >>> > >>> - delegations: returned immediately on detection of any > >>> conflict. The current behavior in the sync case looks > >>> reasonable to me. > >>> - allocation failures: not really sure it's the best error, but > >>> it seems to be all the protocol offers. We probably don't > >>> care much what the client does in this case. > >>> - some rare cases that would probably indicate bugs (e.g., > >>> attempting to destroy a client while other rpc's from that > >>> client are running.) Again we don't care what the client does > >>> here. > >>> - the 4.1 slot-inuse case. > >>> > >>> We also by default map four errors (ETIMEDOUT, EAGAIN, EWOULDBLOCK, > >>> ENOMEM) to delay. I thought I remembered one of those being used by > >>> some HFS system, but can't actually find an example now. A quick grep > >>> doesn't show anything interesting. > >> > >> It's worth mentioning that servers that have frozen state (say, in preparation for Transparent State Migration) may use NFS4ERR_DELAY to prevent clients from modifying open or lock state until that state has transitioned to a destination server. > > > > I thought they'd decided they'll be forced to find a different way to do > > that? > > > > (The issue being that it only works if you're using 4.1, and if the > > session state itself isn't part of the state to be transferred. > > Otherwise you're forced to modify the state anyway since NFS4ERR_DELAY > > is seqid-modifying.) > > The answer is not to return NFS4ERR_DELAY on seqid-modifying operations. > > The source server can return NFS4ERR_DELAY to the client's migration recovery operations (the GETATTR(fs_locations) request) for example. > > Or, the server could return it on the initial PUTFH operation in a compound containing seqid-modifying operations. Oh, right, I'd forgotten that approach.... --b. -- 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
