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. > 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), 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. -- 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
