[Gluster-devel] Problems with ec/nfs.t in regression tests

Thu Feb 12 18:37:50 UTC 2015

On Thu, Feb 12, 2015 at 11:39:51PM +0530, Pranith Kumar Karampuri wrote:
> 
> On 02/12/2015 11:34 PM, Pranith Kumar Karampuri wrote:
> >
> >On 02/12/2015 08:15 PM, Xavier Hernandez wrote:
> >>I've made some more investigation and the problem seems worse.
> >>
> >>It seems that NFS sends a huge amount of requests without waiting for
> >>answers (I've had more than 1400 requests ongoing). Probably there will
> >>be many factors that can influence on the load that this causes, and one
> >>of them could be ec, but it's not related exclusively to ec. I've
> >>repeated the test using a replica 3 and a replica 2 volumes and the
> >>problem still happens.
> >>
> >>The test basically writes a file to an NFS mount using 'dd'. The file
> >>has a size of 1GB. With a smaller file, the test passes successfully.
> >Using NFS client and gluster NFS server on same machine with BIG file dd
> >operations is known to cause hangs. anon-fd-quota.t used to give similar
> >problems so we changed the test to not involve NFS mounts.
> I don't re-collect the exact scenario. Avati found the deadlock of memory
> allocation, when I just joined gluster, in 2010. Raghavendra Bhat raised
> this bug then. CCed him to the thread as well if he knows the exact
> scenario.

This is a well know issue. When a system is under memory pressure, it
will try to flush dirty pages from the VFS. The NFS-client will send the
dirty pages over the network to the NFS-server. Unfortunately, the
NFS-server needs to allocate memory for the handling or the WRITE
procedures. This causes a loop and will most often get the system into a
hang situation.

Mounting with "-o sync", or flushing outstanding I/O from the client
side should normally be sufficient to prevent these issues.

Niels

> 
> Pranith
> >
> >Pranith
> >>
> >>One important thing to note is that I'm not using powerful servers (a
> >>dual core Intel Atom), but this problem shouldn't happen anyway. It can
> >>even happen on more powerful servers if they are busy doing other things
> >>(maybe this is what's happening on jenkins' slaves).
> >>
> >>I think that this causes some NFS requests to timeout. This can be seen
> >>in /var/log/messages (there are many of these messages):
> >>
> >>Feb 12 15:18:45 celler01 kernel: nfs: server gf01.datalab.es not
> >>responding, timed out
> >>
> >>nfs log also has many errors:
> >>
> >>[2015-02-12 14:18:45.132905] E [rpcsvc.c:1257:rpcsvc_submit_generic]
> >>0-rpc-service: failed to submit message (XID: 0x7be78dbe, Program: NFS3,
> >>ProgVers: 3, Proc: 7) to rpc
> >>-transport (socket.nfs-server)
> >>[2015-02-12 14:18:45.133009] E [nfs3.c:565:nfs3svc_submit_reply]
> >>0-nfs-nfsv3: Reply submission failed
> >>
> >>Additionally this causes disconnections from NFS that are not correctly
> >>handled causing that a thread gets stuck in an infinite loop (I haven't
> >>analyzed this problem deeply, but it seems like an attempt to use an
> >>already disconnected socket). After a while, I get this error on the nfs
> >>log:
> >>
> >>[2015-02-12 14:20:19.545429] C
> >>[rpc-clnt-ping.c:109:rpc_clnt_ping_timer_expired] 0-patchy-client-0:
> >>server 192.168.200.61:49152 has not responded in the last 42 seconds,
> >>disconnecting.
> >>
> >>The console executing the test shows this (nfs.t is creating a replica 3
> >>instead of a dispersed volume):
> >>
> >># ./run-tests.sh tests/basic/ec/nfs.t
> >>
> >>... GlusterFS Test Framework ...
> >>
> >>Running tests in file ./tests/basic/ec/nfs.t
> >>[14:12:52] ./tests/basic/ec/nfs.t .. 8/10 dd: error writing
> >>‘/mnt/nfs/0/test’: Input/output error
> >>[14:12:52] ./tests/basic/ec/nfs.t .. 9/10
> >>not ok 9
> >>[14:12:52] ./tests/basic/ec/nfs.t .. Failed 1/10 subtests
> >>[14:27:41]
> >>
> >>Test Summary Report
> >>-------------------
> >>./tests/basic/ec/nfs.t (Wstat: 0 Tests: 10 Failed: 1)
> >>Failed test: 9
> >>Files=1, Tests=10, 889 wallclock secs ( 0.13 usr 0.02 sys + 1.29 cusr
> >>3.45 csys = 4.89 CPU)
> >>Result: FAIL
> >>Failed tests ./tests/basic/ec/nfs.t
> >>
> >>Note that the test takes almost 15 minutes to complete.
> >>
> >>Is there any way to limit the number of requests NFS sends without
> >>having an answer ?
> >>
> >>Xavi
> >>
> >>On 02/11/2015 04:20 PM, Shyam wrote:
> >>>On 02/11/2015 09:40 AM, Xavier Hernandez wrote:
> >>>>Hi,
> >>>>
> >>>>it seems that there are some failures in ec/nfs.t test on regression
> >>>>tests. Doing some investigation I've found that before applying the
> >>>>multi-threaded patch (commit 5e25569e) the problem does not seem to
> >>>>happen.
> >>>
> >>>This has in interesting history in failures, on the regression runs for
> >>>the MT epoll this (i.e ec/nfs.t) did not fail (there were others, but
> >>>not nfs.t).
> >>>
> >>>The patch that allows configuration of MT epoll is where this started
> >>>failing around Feb 5th (but later passed). (see patchset 7 failures on,
> >>>http://review.gluster.org/#/c/9488/ )
> >>>
> >>>I state the above, as it may help narrowing down the changes in EC
> >>>(maybe) that could have caused it.
> >>>
> >>>Also in the latter commit, there was an error configuring the number of
> >>>threads so all regression runs would have run with a single epoll
> >>>thread
> >>>(the MT epoll patch had this hard coded, so that would have run with 2
> >>>threads, but did not show up the issue (patch:
> >>>http://review.gluster.org/#/c/3842/)).
> >>>
> >>>Again I state the above, as this should not be exposing a
> >>>race/bug/problem due to the multi threaded nature of epoll, but of
> >>>course needs investigation.
> >>>
> >>>>
> >>>>I'm not sure if this patch is the cause or it has revealed some bug in
> >>>>ec or any other xlator.
> >>>
> >>>I guess we can reproduce this issue? If so I would try setting
> >>>client.event-threads on master branch to 1, restarting the volume and
> >>>then running the test (as a part of the test itself maybe) to eliminate
> >>>the possibility that MT epoll is causing it.
> >>>
> >>>My belief on MT epoll causing it is in doubt as the runs failed on the
> >>>http://review.gluster.org/#/c/9488/ (configuration patch), which had
> >>>the
> >>>thread count as 1 due to a bug in that code.
> >>>
> >>>>
> >>>>I can try to identify it (any help will be appreciated), but it may
> >>>>take
> >>>>some time. Would it be better to remove the test in the meantime ?
> >>>
> >>>I am checking if this is reproducible on my machine, so that I can
> >>>possibly see what is going wrong.
> >>>
> >>>Shyam
> >>>_______________________________________________
> >>>Gluster-devel mailing list
> >>>Gluster-devel at gluster.org
> >>>http://www.gluster.org/mailman/listinfo/gluster-devel
> >>_______________________________________________
> >>Gluster-devel mailing list
> >>Gluster-devel at gluster.org
> >>http://www.gluster.org/mailman/listinfo/gluster-devel
> >
> >_______________________________________________
> >Gluster-devel mailing list
> >Gluster-devel at gluster.org
> >http://www.gluster.org/mailman/listinfo/gluster-devel
> 