Return-Path: linux-nfs-owner@vger.kernel.org Received: from ipmail06.adl2.internode.on.net ([150.101.137.129]:57881 "EHLO ipmail06.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752485AbaDXBVV (ORCPT ); Wed, 23 Apr 2014 21:21:21 -0400 Date: Thu, 24 Apr 2014 11:20:22 +1000 From: Dave Chinner To: NeilBrown Cc: Jan Kara , Jeff Layton , Trond Myklebust , "J. Bruce Fields" , Mel Gorman , Andrew Morton , linux-mm@kvack.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH/RFC 0/5] Support loop-back NFS mounts - take 2 Message-ID: <20140424012022.GX15995@dastard> References: <20140423022441.4725.89693.stgit@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20140423022441.4725.89693.stgit@notabene.brown> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Apr 23, 2014 at 12:40:58PM +1000, NeilBrown wrote: > This is a somewhat shorter patchset for loop-back NFS support than > last time, thanks to the excellent feedback and particularly to Dave > Chinner. Thanks. > > Avoiding the wait-for-congestion which can trigger a livelock is much > the same, though I've reduced the cases in which the wait is > by-passed. > I did this using current->backing_dev_info which is otherwise serving > no purpose on the current kernel. > > Avoiding the deadlocks has been turned on its head. > Instead of nfsd checking if it is a loop-back mount and setting > PF_FSTRANS, which then needs lots of changes too PF_FSTRANS and > __GFP_FS handling, it is now NFS which checks for a loop-back > filesystem. > > There is more verbosity in that patch (Fifth of Five) but the essence > is that nfs_release_page will now not wait indefinitely for a COMMIT > request to complete when sent to the local host. It still waits a > little while as some delay can be important. But it won't wait > forever. > The duration of "a little while" is currently 100ms, though I do > wonder if a bigger number would serve just as well. > > Unlike the previous series, this set should remove deadlocks that > could happen during the actual fail-over process. This is achieved by > having nfs_release_page monitor the connection and if it changes from > a remote to a local connection, or just disconnects, then it will > timeout. It currently polls every second, though this probably could > be longer too. It only needs to be the same order of magnitude as the > time it takes node failure to be detected and failover to happen, and > I suspect that is closer to 1 minute. So maybe a 10 or 20 second poll > interval would be just as good. > > Implementing this timeout requires some horrible code as the > wait_on_bit functions don't support timeouts. If the general approach > is found acceptable I'll explore ways to improve the timeout code. > > Comments, criticism, etc very welcome as always, Looks much less intrusive to me, and doesn't appear to affect any other filesystem or the recursion patterns of memory reclaim, so I like it very much more than the previous patchset. Nice work! :) The code changes are really outside my area of expertise now, so I don't really feel qualified to review the changes. However, consider the overall approach: Acked-by: Dave Chinner Cheers, Dave. -- Dave Chinner david@fromorbit.com