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 <dchinner@xxxxxxxxxx> Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>