Re: 3.12-rcX - NFS regression - kswapd0 / kswapd1 stays using 100%CPU?

[Helge Deller]

On 10/18/2013 09:36 PM, Myklebust, Trond wrote:
> On Fri, 2013-10-18 at 21:26 +0200, Helge Deller wrote:
>> On 10/17/2013 11:07 PM, Myklebust, Trond wrote:
>>> On Thu, 2013-10-17 at 22:42 m, Helge Deller wrote:
>>>> I'm seeing a regression with current kernel git head when using NFS-mounts.
>>>> Architecture in my case is parisc, although I don't think that this is relevant.
>>>> At least kernel 3.10 (and I think 3.11) didn't showed that problem.
>>>>
>>>> The symtom is, that "top" shows high usage of either kswapd0 or kswapd1.
>>>> Here is an output with kswapd1:
>>>>   PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM     TIME COMMAND
>>>>    37 root      20   0     0    0    0 R  91.8  0.0  63:00.40 kswapd1
>>>> 28448 root      20   0  3252 1428 1060 R  15.3  0.0   0:00.09 top
>>>>     1 root      20   0  2784  988  852 S   0.0  0.0   0:09.95 init
>>>>
>>>> This is what ps shows:
>>>> lsXXXX:~# ps -ef |  grep mount
>>>> root      1181     1  0 14:51 ?        00:00:18 /usr/sbin/automount --pid-file /var/run/autofs.pid
>>>> root     25331  1181  0 21:25 ?        00:00:00 /bin/mount -n -t nfs -s -o nolock,rw,hard,intr homes:/unixhome1 /net/home1
>>>> root     25332 25331  0 21:25 ?        00:00:00 /sbin/mount.nfs homes:/unixhome1 /net/home1 -s -n -o rw,nolock,hard,intr
>>>>
>>>> And using sysrq to show the blocked tasks I get in syslog:
>>>> SysRq : Show Blocked State
>>>> mount.nfs       D 00000000401040c0     0 25332  25331 0x00000010
>>>> Backtrace:
>>>> [<0000000040113a68>] __schedule
>>>>
>>>> I know it's not a problem of the NFS server, since the same mount is still ok on other machines.
>>>> The NFS directory was already mounted and in use when this mount happened again (called by cron-job). 
>>>>  
>>>> Any ideas?
>>>
>>> If the NFS directory is already mounted, then why is the automounter
>>> trying to mount it a second time?
>>
>> I was wrong in this.
>> The directory wasn't mounted yet (or at least it was unmounted in the meantime before the new
>> mount.nfs was called).
>>
>> I'm now not even sure, that the high kswapd is really triggered by the NFS problem,
>> because I now have another machine with the blocked NFS-mount, but without
>> the high kswapd usage.
>>
>> Nevertheless, the blocked nfs mount tasks really make me wonder. There is clearly
>> some kind of regression since it doesn't happen with older kernels.
> 
> Have you ever reproduced it without the automounter?

No, because it happens only after quite some time (>12h) and only if I have it
under pressure (load is >9 on a 4-way box).

I'll try it as soon as possible.

> Also, could you please try a sysRQ-t the next time it happens, so that
> we can get a trace of where the mount program is hanging. Knowing that
> the mount is stuck in "__schedule()" is not really interesting unless we
> know from where that was called.

Actually, the machine was still running in this state.
Here is sysrq-t:
[112009.084000] mount           S 00000000401040c0     0 25331      1 0x00000010
[112009.084000] Backtrace:
[112009.084000]  [<0000000040113a68>] __schedule+0x500/0x810
[112009.232000]
[112009.232000] mount.nfs       D 00000000401040c0     0 25332  25331 0x00000010
[112009.232000] Backtrace:
[112009.232000]  [<0000000040113a68>] __schedule+0x500/0x810

Helge
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