On Apr 25, 2013, at 2:46 PM, "bfie...@fieldses.org" <bfie...@fieldses.org> wrote:
> On Thu, Apr 25, 2013 at 02:40:11PM -0400, Chuck Lever wrote: >> >> On Apr 25, 2013, at 2:19 PM, "bfie...@fieldses.org" <bfie...@fieldses.org> >> wrote: >> >>> On Thu, Apr 25, 2013 at 02:10:36PM +0000, Myklebust, Trond wrote: >>>> On Thu, 2013-04-25 at 09:49 -0400, bfie...@fieldses.org wrote: >>>>> On Thu, Apr 25, 2013 at 01:30:58PM +0000, Myklebust, Trond wrote: >>>>>> On Thu, 2013-04-25 at 09:29 -0400, bfie...@fieldses.org 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. -- Chuck Lever chuck[dot]lever[at]oracle[dot]com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
