Re: System CPU increasing on idle 2.6.36

[Mark Moseley]

On Fri, Jan 7, 2011 at 10:05 AM, Mark Moseley <moseleymark@xxxxxxxxx> wrote:
> On Wed, Jan 5, 2011 at 11:43 AM, Mark Moseley <moseleymark@xxxxxxxxx> wrote:
>> 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.
>>
>
> NOTE: NFS/Kernel guys: I've left the 2.6.36.2 box still thrashing
> about in case there's something you'd like me to look at.
>
> Ok, both my 2.6.36.2 kernel box and my 2.6.35->2.6.36 bisect box (was
> bisected to ce7db282a3830f57f5b05ec48288c23a5c4d66d5 -- this is my
> first time doing bisect, so I'll preemptively apologize for doing
> anything silly) both went berserk within 15 mins of each other, after
> an uptime of around 63 hours for 2.6.36.2 and 65 hours for the
> bisected box. The 2.6.36.2 one is still running with all the various
> flush-0:xx threads spinning wildly. The bisected box just keeled over
> and died, but is back up now. The only kernel messages logged are just
> of the "task kworker/4:1:359 blocked for more than 120 seconds"
> variety, all with _raw_spin_lock_irq at the top of the stack trace.
>
> Looking at slabinfo, specifically, this: stats=$(grep nfs_inode_cache
> /proc/slabinfo | awk '{ print $2, $3 }')
> the active_objs and num_objs both increase to over a million (these
> boxes are delivering mail to NFS-mounted mailboxes, so that's
> perfectly reasonable). On both boxes, looking at sar, things start to
> go awry around 10am today EST. At that time on the 2.6.36.2 box, the
> NFS numbers look like this:
>
> Fri Jan  7 09:58:00 2011: 1079433 1079650
> Fri Jan  7 09:59:00 2011: 1079632 1080300
> Fri Jan  7 10:00:00 2011: 1080196 1080300
> Fri Jan  7 10:01:01 2011: 1080599 1080716
> Fri Jan  7 10:02:01 2011: 1081074 1081288
>
> on the bisected, like this:
>
> Fri Jan  7 09:59:34 2011: 1162786 1165320
> Fri Jan  7 10:00:34 2011: 1163301 1165320
> Fri Jan  7 10:01:34 2011: 1164369 1165450
> Fri Jan  7 10:02:35 2011: 1164179 1165450
> Fri Jan  7 10:03:35 2011: 1165795 1166958
>
> When the bisected box finally died, the last numbers were:
>
> Fri Jan  7 10:40:33 2011: 1177156 1177202
> Fri Jan  7 10:42:21 2011: 1177157 1177306
> Fri Jan  7 10:44:55 2011: 1177201 1177324
> Fri Jan  7 10:45:55 2011: 1177746 1177826
>
> On the still-thrashing 2.6.36.2 box, the highwater mark is:
>
> Fri Jan  7 10:23:30 2011: 1084020 1084070
>
> and once things went awry, the active_objs started falling away and
> the number_objs has stayed at 1084070. Last numbers were:
>
> Fri Jan  7 12:19:34 2011: 826623 1084070
>
> The bisected box had reached 1mil entries (or more significantly
> 1048576 entries) by y'day evening. The 2.6.36.2 box hit that by 7am
> EST today. So in neither case was there a big spike in entries.
>
> These boxes have identical workloads. They're not accessible from the
> net, so there's no chance of a DDoS or something. The significance of
> 10am EST could be either uptime-related (all these have gone down
> after 2-3 days) or just due to the to-be-expected early morning spike
> in mail flow.
>

Actually, I shouldn't say 'perfectly reasonable'. On other boxes in
that pool, doing the same workload (but running 2.6.32.27), the number
is more like:

117196 120756

after 9 days of uptime. So maybe 8 x that  isn't quite reasonable
after only 2.5 days of uptime.
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