vnode leak in FFS code ... ?

Marc G. Fournier
Fri, 03 Sep 2004 20:49:17 -0000

Just as a followup to this ... the server crashed on Thursday night around
22:00ADT, only just came back up after a very long fsck ... with all 62
VMs started up, and 1008 processes running, vnodes currently look like:

Sep  4 00:43:00 venus root: debug.numvnodes: 58370 - debug.freevnodes: 824 -
debug.vnlru_nowhere: 0 - vlruwt
Sep  4 00:44:00 venus root: debug.numvnodes: 58370 - debug.freevnodes: 782 -
debug.vnlru_nowhere: 0 - vlruwt
Sep  4 00:45:01 venus root: debug.numvnodes: 58370 - debug.freevnodes: 977 -
debug.vnlru_nowhere: 0 - vlruwt
Sep  4 00:46:00 venus root: debug.numvnodes: 58370 - debug.freevnodes: 582 -
debug.vnlru_nowhere: 0 - vlruwt
venus# ps aux | wc -l
     1008
venus#

about a tenth of what they were when the server crashed :(



On Wed, 1 Sep 2004, Marc G. Fournier wrote:

> On Wed, 1 Sep 2004, Allan Fields wrote:
>
>>> It's really hard to tell if there is a vnode leak here.  The
vnode pool
>>> is fairly fluid and has nothing to do with the number of files that
are
>>> actually 'open'.  Vnodes get created when the VFS layer
wants to access
>>> an object that isn't already in the cache, and only get
destroyed when
>>> the object is destroyed.  A vnode that reprents a file that was
opened
>>> will stay 'active' in the system long after the file has
been closed,
>>> because it's cheaper to keep it active in the cache than it is
to
>>> discard it and then risk having to go through the pain of a namei()
>>> and VOP_LOOKUP() again later.  Only if the maxvnode limit is hit
will
>>> old vnodes start getting recycled to represent other objects.
[...]
>>>
>>> So you've obviously bumped up kern.maxvnodes well above the
limits that
>>> are normally generated from the auto-tuner.  Why did you do that,
if not
>>> because you knew that you'd have a large working set of
referenced (but
>>> maybe not open all at once) filesystem objects?  [...]
>>
>> There was a pevious thread I've found which also helps explains
>> this further:
>> http://lists.freebsd.org/pipermail/freebsd-stable/2003-May/001266.html
>>
>> Really the same issue now as then?
>
> I'm not getting the hangs now, it is freeing up vnodes ... but its
having to
> work very hard to do so, or so it seems:
>
> venus# ps aux | grep vnlru
> root        7  3.0  0.0     0    0  ??  DL    5Aug04 606:34.54  (vnlru)
>
> I started up the script for monitoring this on Aug 29th ... since then,
there
> have been 4331 entries to the log file, of which  1927 are in
'vlrup', which
> I believe is vnlru running through its lists trying to find some to free
up,
> if I recall the code ... ?
>
> venus# grep vnode /var/log/syswatch | wc -l
>    4331
> venus# grep vnode /var/log/syswatch | grep vlrup | wc -l
>    1927
>
> and this is based on a check every minute ...
>
> The other server, running ~19 more VMs (~100 more processes), only up 2
days
> now, seems to be fairing better:
>
> debug.numvnodes: 344062 - debug.freevnodes: 168285 - debug.vnlru_nowhere: 0
-
> vlruwt
>
> I've schedualed 'maintenance' on that server for Saturday ...
am going to
> shut down all 'non-host server' processes, and unmount the large
file system
> (where all the VMs run off of) ... see if that cleans up any of the vnodes
> without having to do a reboot ...
>
> If that doesn't work, I could cause a panic and have it dump core, if
that
> would provide for easier/better debugging ... ?
>
> I have limited flexibility with the server, but it is a 'real'
server without
> a fake load on it, and as solid as I've always considered FreeBSD to
be, I
> seem to have a knack for pushing it and breaking it :( ... so whatever data
I
> can provide to make it that much more solid, even if it involves a little
bit
> of downtime to get a good core dump, I'm willing to do ...
>
> ----
> Marc G. Fournier           Hub.Org Networking Services (http://www.hub.org)
> Email: scrappy@hub.org           Yahoo!: yscrappy              ICQ: 7615664
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----
Marc G. Fournier           Hub.Org Networking Services (http://www.hub.org)
Email: scrappy@hub.org           Yahoo!: yscrappy              ICQ: 7615664