4.11-STABLE leaks vnodes worse then 4.x from Feb 13th ... ?

[Marc G. Fournier]

Recently, I started having problems with one of my newest servers ... 
figuring that it might have somethign to do with the fact that I went SATA 
for this one (all others are SCSI), I figured it might be a driver issue 
causing the problems, since everything else is the same as the other 5 
servers on our network ...

Today, I'm starting to wonder if I've been just looking at the "most 
obvious" cause, instead of looking deeper ...

The problem that manifests itself is similar to the old 'ran out of vnode' 
issue I used to experience under 4.x ... the server would still run, be 
totally pingable, and you could even get the motd when you tried to ssh 
in, but you couldn't get a prompt, and all processes were hung ...

I just upgraded the kernel on this machine (mercury) on the 13th of July, 
and its been running 1 day, 12 hrs now ... there is hardly anything 
running on this machine (10 jails), and vnode usage is:

debug.numvnodes: 336460 - debug.freevnodes: 5275 - debug.vnlru_nowhere: 0 - vlruwt

One of my older servers (neptune), running kernels from Feb 13th of this 
year, and with 81 jails running on it, is using up *significantly less* 
vnodes (uptime: 1 day, 10 hours):

debug.numvnodes: 279710 - debug.freevnodes: 91442 - debug.vnlru_nowhere: 0 - vlruwt

Now, compared to neptune, mercury isn't running anything special ... 
several apache 1 processes, postfix, cyrus-imapd and that's it ... 
neptune on the other hand, is running the full gambit ... aolserver, java, 
apache 1 and 2, postfix, etc ...

So, I'm starting to think that the problem isn't "hardware related", but 
the kernel itself ... the latest 4.11-STABLE kernel seems to have brought 
in new vnode leakage, or ... vnlru isn't working as it should be to free 
up vnodes ...

Looking at that process on mercury:

# ps aux | grep vnlru
root        7  0.0  0.0     0    0  ??  DL   Wed11PM   0:00.65  (vnlru)

whereas on neptune:

# ps aux | grep vnlru
root          9  0.0  0.0     0    0  ??  DL   Thu01AM   0:00.79  (vnlru)

so about the same about of CPU time being expended ... a bit more on the 
more loaded server, but not a major amount ...

I'd like to try and debug this, but don't know where to start ... I 
realize that 4.x isn't being pushed anymore, but there are alot of us that 
haven't moved to 5.x yet (am working on that for our next server, but its 
going to take me several months before I can convert all our existing 
servers up) ...

I do have a serial console on this server, if that helps to debug things 
...

I've heard that there was some work done on 5.x to clean up some of the 
vnode leaks ... not sure if that is fact or just rumor ... but, if so, 
would any of them be MFCable to 4.x?

Thanks ...

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Marc G. Fournier           Hub.Org Networking Services (http://www.hub.org)
Email: scrappy at hub.org           Yahoo!: yscrappy              ICQ: 7615664