On Fri, Sep 12, 2014 at 11:54:17AM -0400, Trond Myklebust wrote: > On Fri, Sep 12, 2014 at 11:21 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > On Fri, Sep 12, 2014 at 10:36:21AM -0400, J. Bruce Fields wrote: > >> On Fri, Sep 12, 2014 at 10:21:53AM -0400, Jeff Layton wrote: > >> > Grace period > >> > eventually ends, and its record is purged from the DB. > >> > > >> > Now we have a client that has reclaimed some files but that has no > >> > record on stable storage. > >> > > >> > One possibility is to prematurely expire v4.1+ clients that have not > >> > sent a RECLAIM_COMPLETE when the grace period ends. > >> > > >> > That seems problematic though -- what about clients that just happen to > >> > do an EXCHANGE_ID just before the grace period is going to end, and > >> > that get expired before they can issue their RECLAIM_COMPLETE. Will > >> > that be a problem for them? > >> > >> In that case a client will send a reclaim, get back a NO_GRACE error, > >> mark the rest of its state as unrecoverable, send the RECLAIM_COMPLETE, > >> and continue normally. (To the extent it can--signalling affected > >> processes or EIOing further attempts to use the unreclaimed state, or > >> whatever.) > > > > The one thing the server *could* do in this sort of case is extend the > > grace period by a little--I seem to recall the spec giving some leeway > > for this kind of thing. > > > Section 8.4.2.1. Thanks! http://tools.ietf.org/html/rfc5661#section-8.4.2.1 "Some additional time in order to allow a client to establish a new client ID and session and to effect lock reclaims may be added to the lease time." I thought there was something else but I actually must have been remembering the "diligently flushing" language describing delegation recalls. Anyway. > > > So for example the server could have a heuristics like: extend the grace > > period by another second each time we notice there's been an EXCHANGE_ID > > or reclaim in the previous second, up to some maximum. And I suppose it > > could also delay the grace period until someone actually attempts a > > non-reclaim open. > > > > In isolation a single client slipping in the end like that sounds like a > > freak event, but if there's a ton of state to reclaim perhaps it could > > become more likely. > > > > I don't think that's a priority, we might just want to make sure we know > > how to do that in the future. > > > > But now that I think about it I don't see the existing or proposed > > nfsdcltrack stuff tying our hands in any way here. It just gives the > > kernel some extra information, and the kernel still has discretion about > > when exactly it wants to end the grace period. > > > > It is even allowed to grant reclaim lock attempts after the grace > period has ended _if_ and only if it can guarantee that no conflicting > locks were issued. > > However note that the NFSv4.1 client is not actually allowed to issue > non-reclaim lock requests before it has issued a RECLAIM_COMPLETE. I > dunno how religiously we stick to that in Linux (I think we do), Yes, the server strictly enforces this so we'd know if the client skipped the RECLAIM_COMPLETE. (Any open would fail over 4.1.) > but the point is that the server can and should rely on the client > _always_ sending a RECLAIM_COMPLETE if it is going to establish new > locks. Yes. --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
