On Wed, Sep 01, 2010 at 03:11:23PM -0600, Tim Gardner wrote: > On 09/01/2010 02:55 PM, Neil Brown wrote: > >On Wed, 1 Sep 2010 12:54:01 -0400 > >"J. Bruce Fields"<bfields@xxxxxxxxxxxx> wrote: > > > >>On Wed, Sep 01, 2010 at 09:39:55AM -0600, Tim Gardner wrote: > >>>I've been pursuing a simple reproducer for an NFS lockup that shows > >>>up under stress. There is a bunch of info (some of it extraneous) in > >>>http://bugs.launchpad.net/bugs/561210. I can reproduce it by writing > >>>loop mounted NFS exports: > >>> > >>>/etc/fstab: 127.0.0.1:/srv /mnt/srv nfs rw 0 2 > >>>/etc/exports: /srv 127.0.0.1(rw,insecure,no_subtree_check) > >>> > >>>See the attached scripts test_master.sh and test_client.sh. I simply > >>>repeat './test_master.sh wait' until nfsd locks up, typically within > >>>1-3 cycles, e.g., > >> > >>Without looking at the dmesg and scripts carefully to confirm, one > >>possible explanation is a deadlock when the server can't allocate memory > >>required to service client requests, memory which the client itself > >>needs to free by writing back dirty pages, but can't because the server > >>isn't processing its writes. > > > >Having looked closely I'd say it is almost certainly this issue. > >nfsd thread 1266 is in zone_reclaim waiting on a page to be written out so > >the memory can be reused. > >The other nfsd threads are blocking on a mutex held by 1266. > >The dd processes are waiting for pages to be written to the server > > > >The particular page that 1266 is waiting on is almost certainly a page on an > >NFS file, so you have a cyclic deadlock. > > > >> > >>For that reason we just don't support loopback mounts--they're OK for > >>light testing, but it would be difficult to make them completely robust > >>under load. > > > >I wonder if we could use 'containers' to partition available memory between > >'nfsd threads' and 'everything else'?? Probably not worth the effort. > > > >NeilBrown > > > > I'm currently working with my support folks to reproduce this using > the exact same configuration as the customer, e.g., an NFS server > (running as a guest on a VMWare ESX host) serving multiple gigabit > clients. > > I assume that is a reasonable scenario? Assuming no VMWare problem (which I know nothing about), sure. --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
