Re: System CPU increasing on idle 2.6.36

[Mark Moseley]

On Tue, Jan 4, 2011 at 1:40 PM, Simon Kirby <sim@xxxxxxxxxx> wrote:
> On Tue, Jan 04, 2011 at 09:42:14AM -0800, Mark Moseley wrote:
>
>> On Wed, Dec 29, 2010 at 2:03 PM, Simon Kirby <sim@xxxxxxxxxx> wrote:
>>
>> > I've noticed nfs_inode_cache is ever-increasing as well with 2.6.37:
>> >
>> > ?OBJS ACTIVE ?USE OBJ SIZE ?SLABS OBJ/SLAB CACHE SIZE NAME
>> > 2562514 2541520 ?99% ? ?0.95K ?78739 ? ? ? 33 ? 2519648K nfs_inode_cache
>> > 467200 285110 ?61% ? ?0.02K ? 1825 ? ? ?256 ? ? ?7300K kmalloc-16
>> > 299397 242350 ?80% ? ?0.19K ?14257 ? ? ? 21 ? ? 57028K dentry
>> > 217434 131978 ?60% ? ?0.55K ? 7767 ? ? ? 28 ? ?124272K radix_tree_node
>> > 215232 ?81522 ?37% ? ?0.06K ? 3363 ? ? ? 64 ? ? 13452K kmalloc-64
>> > 183027 136802 ?74% ? ?0.10K ? 4693 ? ? ? 39 ? ? 18772K buffer_head
>> > 101120 ?71184 ?70% ? ?0.03K ? ?790 ? ? ?128 ? ? ?3160K kmalloc-32
>> > ?79616 ?59713 ?75% ? ?0.12K ? 2488 ? ? ? 32 ? ? ?9952K kmalloc-128
>> > ?66560 ?41257 ?61% ? ?0.01K ? ?130 ? ? ?512 ? ? ? 520K kmalloc-8
>> > ?42126 ?26650 ?63% ? ?0.75K ? 2006 ? ? ? 21 ? ? 32096K ext3_inode_cache
>> >
>> > http://0x.ca/sim/ref/2.6.37/inodes_nfs.png
>> > http://0x.ca/sim/ref/2.6.37/cpu2_nfs.png
>> >
>> > Perhaps I could bisect just fs/nfs changes between 2.6.35 and 2.6.36 to
>> > try to track this down without having to wait too long, unless somebody
>> > can see what is happening here.
>>
>> I'll get started bisecting too, since this is something of a
>> show-stopper. Boxes that pre-2.6.36 would stay up for months at a time
>> now have to be powercycled every couple of days (which is about how
>> long it takes for this behavior to show up). This is across-the-board
>> for about 50 boxes, ranging from 2.6.36 to 2.6.36.2.
>>
>> Simon: It's probably irrelevant since these are kernel threads, but
>> I'm curious what distro your boxes are running. Ours are Debian Lenny,
>> i386, Dell Poweredge 850s. Just trying to figure out any
>> commonalities. I'll get my boxes back on 2.6.36.2 and start watching
>> nfs_inode_cache as well.
>
> Same distro, x86_64, similar servers.
>
> I'm not sure if the two cases I am seeing are exactly the same problem,
> but on the log crunching boxes, system time seems proportional to
> nfs_inode_cache and nfs_inode_cache just keeps growing forever; however,
> if I stop the load and unmount the NFS mount points, all of the
> nfs_inode_cache objects do actually go away (after umount finishes).
>
> It seems the shrinker callback might not be working as intended here.
>
> On the shared server case, the crazy spinlock contention from all of the
> flusher processes happens suddenly and overloads the boxes for 10-15
> minutes, and then everything recovers.  Over 21 of these boxes, they
> each have about 500k-700k nfs_inode_cache objects.  The log cruncher hit
> 3.3 million nfs_inode_cache objects before I unmounted.
>
> Are your boxes repeating this behaviour at any predictable interval?

Simon:
My boxes definitely fall into the latter category, with spinlock
regularly sitting at 60-80% CPU (according to 'perf top'). As far as
predictability, not strictly, but it's typically after an uptime of
2-3 days. They take so long to get into this state that I've never
seen the actual transition in person, just the after-effects of
flush-0:xx gone crazy. These boxes have a number of other NFS mounts,
but it's on the flush-0:xx's for the heavily written-to NFS mounts
that are spinning wildly, which you'd expect to be the case. The
infrequently written-to NFS servers' flush-0:xx isn't to be found in
'top' output.

I'd booted into older kernels after my initial reply, so I'm 14 hrs
into booting a box back into 2.6.36.2 and another box into a
double-bisected 2.6.35-2.6.36 kernel (my first bisect hit compile
errors). Both are running normally but that fits with the pattern so
far.

NFS Guys:
Anything else we can be digging up to help debug this? This is a
pretty ugly issue.
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