[Bug 561210] Re: Writing big files to NFS target causes system lock up

[JimWright]

Hi Tim,

After your post I retried my test case (see comment #23 above), except
this time using KVM instead of VMWare Server.  All details of the
virtual machine, i.e. 2xCPU/512MB RAM/8GB HDD are the same - it's just
using KVM instead of VMWare.

I can confirm that under KVM and a vanilla install of 10.04(.0) the
problem occurs exactly as I described before, and within seconds.  This
is using a 64bit kernel version 2.6.32-21.32.

I then upgraded the virtual machine to the latest kernel 2.6.32-24.41
and ran the same test case again.  This kernel seemed much more stable
and did not exhibit problems.  Multiple iterations of the gzip loop ran
successfully.  So I  tried running a second loop of gzip processes.
Thus there are now two gzip processes both accessing the NFS mount
After a minute or so this caused the issue to occur together with the
same messages appearing in syslog, the load skyrocketing and the system
freezing.  So whilst 2.6.32-24.41 appears to me to be better, I do not
believe the fundamental problem has been solved.  Repeating the test
subsequent times, it sometimes took two simultaneous gzip processes to
trigger the error, and other times three.  I used the following script
to run the gzip processes:

#!/bin/bash
while true
do
    gzip -c /mnt/srv/test >/mnt/srv/test$$.gz
done

If I could also make a couple of observations.  Everyone I have seen
having this issue (or issues that look in my opinion suspiciously close
to this one) seems to be running a 64bit kernel - I have not tested a
32bit kernel.  My test case uses the loopback interface, so switch speed
and/or network card should be irrelevant.  Also having an amount of load
on the NFS client seems to be important, that is why my test case
attempts to gzip a file of random data.  I'm not sure your simple dd
would generate enough of a real workload.

Jim

BTW In the original test case I missed out a "chmod 777 /srv", but that
really isn't going to change anything.

-- 
Writing big files to NFS target causes system lock up
https://bugs.launchpad.net/bugs/561210
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