On Tue, 2011-11-22 at 12:02 +0000, Andrew Cooper wrote: > On 22/11/11 11:38, Trond Myklebust wrote: > > On Mon, 2011-11-21 at 18:14 +0000, Andrew Cooper wrote: > >> Following some debugging, I believe that the attached patch fixes the > >> problem. > >> > >> Simply returning EAGAIN is not sufficient, as the task does not get > >> requeued, and times out 13 seconds later (as per our mount options). > >> Setting the SOCK_ASYNC_NOSPACE bit causes the requeue to happen. > >> > >> I realize that this is a gross hack and I should probably not be using > >> SOCK_ASYNC_NOSPACE in that way. Is there a better way to achieve the > >> same solution? > >> > > What you are doing will cause the request to be put to sleep with no > > guarantee that it will ever be woken up. Why would we want to do that if > > there is no report of a tcp window/buffer space congestion? > > But the reason we get to this code is because there was a report of > space collision. What would you suggest instead? Changing > xs_{tcp,udp}_send_request() to retry in this case would defeat the point > of having xs_nospace(). I suggest doing absolutely nothing: do what you originally proposed, which is to report the EAGAIN so that the client state machine retries the socket write. My point is that this is a context which is _not_ atomic with the original report of tcp window/buffer space congestion. There are no locks or anything else that will guarantee that the congestion still exists, and the fact that the SOCK_ASYNC_NOSPACE flag is now clear indicates that this is the case. The whole purpose of xs_nospace() is to wait until a congestion condition clears. If the congestion clears before we get here, then we have no reason to do anything special other than retry. Trond -- 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