vmdaemon CPU usage and poor performance in 10.0-RELEASE
Alan Cox
alc at rice.edu
Wed Aug 20 16:27:04 UTC 2014
On 08/20/2014 11:22, Polyack, Steve wrote:
>> -----Original Message-----
>> From: Alan Cox [mailto:alc at rice.edu]
>> Sent: Wednesday, August 20, 2014 12:09 PM
>> To: Polyack, Steve; freebsd-stable at freebsd.org
>> Subject: Re: vmdaemon CPU usage and poor performance in 10.0-RELEASE
>>
>> On 08/20/2014 10:56, Polyack, Steve wrote:
>>>> -----Original Message-----
>>>> From: Alan Cox [mailto:alc at rice.edu]
>>>> Sent: Wednesday, August 20, 2014 11:55 AM
>>>> To: Polyack, Steve; freebsd-stable at freebsd.org
>>>> Subject: Re: vmdaemon CPU usage and poor performance in 10.0-RELEASE
>>>>
>>>> On 08/20/2014 09:55, Polyack, Steve wrote:
>>>>>> -----Original Message-----
>>>>>> From: Polyack, Steve
>>>>>> Sent: Wednesday, August 20, 2014 9:14 AM
>>>>>> To: Polyack, Steve; Alan Cox; freebsd-stable at freebsd.org
>>>>>> Subject: RE: vmdaemon CPU usage and poor performance in 10.0-
>> RELEASE
>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: owner-freebsd-stable at freebsd.org [mailto:owner-freebsd-
>>>>>>> stable at freebsd.org] On Behalf Of Polyack, Steve
>>>>>>> Sent: Tuesday, August 19, 2014 12:37 PM
>>>>>>> To: Alan Cox; freebsd-stable at freebsd.org
>>>>>>> Subject: RE: vmdaemon CPU usage and poor performance in 10.0-
>>>> RELEASE
>>>>>>>> -----Original Message-----
>>>>>>>> From: owner-freebsd-stable at freebsd.org [mailto:owner-freebsd-
>>>>>>>> stable at freebsd.org] On Behalf Of Alan Cox
>>>>>>>> Sent: Monday, August 18, 2014 6:07 PM
>>>>>>>> To: freebsd-stable at freebsd.org
>>>>>>>> Subject: Re: vmdaemon CPU usage and poor performance in 10.0-
>>>>>> RELEASE
>>>>>>>> On 08/18/2014 16:29, Polyack, Steve wrote:
>>>>>>>>>> -----Original Message-----
>>>>>>>>>> From: owner-freebsd-stable at freebsd.org [mailto:owner-freebsd-
>>>>>>>>>> stable at freebsd.org] On Behalf Of Alan Cox
>>>>>>>>>> Sent: Monday, August 18, 2014 3:05 PM
>>>>>>>>>> To: freebsd-stable at freebsd.org
>>>>>>>>>> Subject: Re: vmdaemon CPU usage and poor performance in 10.0-
>>>>>>> RELEASE
>>>>>>>>>> On 08/18/2014 13:42, Polyack, Steve wrote:
>>>>>>>>>>> Excuse my poorly formatted reply at the moment, but this seems
>> to
>>>>>>>> have
>>>>>>>>>> fixed our problems. I'm going to update the bug report with a
>> note.
>>>>>>>>>>> Thanks Alan!
>>>>>>>>>> You're welcome. And, thanks for letting me know of the outcome.
>>>>>>>>>>
>>>>>>>>> Actually, I may have spoken too soon, as it looks like we're seeing
>>>>>>>> vmdaemon tying up the system again:
>>>>>>>>> root 6 100.0 0.0 0 16 - DL Wed04PM 4:37.95
>>>>>>> [vmdaemon]
>>>>>>>>> Is there anything I can check to help narrow down what may be the
>>>>>>>> problem? KTrace/truss on the "process" doesn't give any
>> information, I
>>>>>>>> suppose because it's actually a kernel thread.
>>>>>>>>
>>>>>>>> Can you provide the full output of top? Is there anything unusual
>>>> about
>>>>>>>> the hardware or software configuration?
>>>>>>> This may have just been a fluke (maybe NFS caching the old
>>>> vm_pageout.c
>>>>>>> during the first source build). We've rebuilt and are monitoring it
>> now.
>>>>>>> The hardware consists of a few Dell PowerEdge R720xd servers with
>>>> 256GB
>>>>>>> of RAM and array of SSDs (no ZFS). 64GB is dedicated to postgres
>>>>>>> shared_buffers right now. FreeBSD 10, PostgreSQL 9.3, Slony-I v2.2.2,
>>>> and
>>>>>>> redis-2.8.11 are all in use here. I can't say that anything is unusual
>> about
>>>>>> the
>>>>>>> configuration.
>>>>>>>
>>>>>> We are still seeing the issue. It seems to manifest once the "Free"
>>>> memory
>>>>>> gets under 10GB (of 256GB on the system), even though ~200GB of this
>> is
>>>>>> classified as Inactive. For us, this was about 7 hours of database
>> activity
>>>>>> (initial replication w/ slony). Right now vmdaemon is consuming 100%
>>>> CPU
>>>>>> and shows 671:34 CPU time when it showed 0:00 up until the problem
>>>>>> manifested. The full top output (that fits on my screen) is below:
>>>>>>
>>>>>> last pid: 62309; load averages: 4.05, 4.24, 4.10
>>>>>> up 0+22:34:31 09:08:43
>>>>>> 159 processes: 8 running, 145 sleeping, 1 waiting, 5 lock
>>>>>> CPU: 14.5% user, 0.0% nice, 4.9% system, 0.0% interrupt, 80.5% idle
>>>>>> Mem: 26G Active, 216G Inact, 4122M Wired, 1178M Cache, 1632M Buf,
>>>> 2136M
>>>>>> Free
>>>>>> Swap: 32G Total, 32G Free
>>>>>>
>>>>>> PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU
>>>>>> COMMAND
>>>>>> 11 root 32 155 ki31 0K 512K CPU31 31 669.6H 2934.23% idle
>>>>>> 6 root 1 -16 - 0K 16K CPU19 19 678:57 100.00% vmdaemon
>>>>>> 1963 pgsql 1 45 0 67538M 208M CPU0 0 121:46 17.38%
>> postgres
>>>>>> 2037 pgsql 1 77 0 67536M 2200K *vm ob 14 6:24 15.97%
>> postgres
>>>>>> 1864 pgsql 1 31 0 67536M 1290M semwai 4 174:41 15.19%
>>>> postgres
>>>>>> 1996 pgsql 1 38 0 67538M 202M semwai 16 120:27 15.09%
>>>> postgres
>>>>>> 1959 pgsql 1 39 0 67538M 204M CPU27 27 117:30 15.09%
>> postgres
>>>>>> 1849 pgsql 1 32 0 67536M 1272M semwai 23 126:22 13.96%
>>>> postgres
>>>>>> 1997 pgsql 1 31 0 67538M 206M CPU30 30 122:26 11.77%
>> postgres
>>>>>> 2002 pgsql 1 34 0 67538M 182M sbwait 11 55:20 11.28%
>> postgres
>>>>>> 1961 pgsql 1 32 0 67538M 206M CPU12 12 121:47 10.99%
>> postgres
>>>>>> 1964 pgsql 1 30 0 67538M 206M semwai 28 122:08 9.86%
>> postgres
>>>>>> 1962 pgsql 1 29 0 67538M 1286M sbwait 2 45:49 7.18%
>> postgres
>>>>>> 1752 root 1 22 0 78356K 8688K CPU2 2 175:46 6.88% snmpd
>>>>>> 1965 pgsql 1 25 0 67538M 207M semwai 9 120:55 6.59%
>> postgres
>>>>>> 1960 pgsql 1 23 0 67538M 177M semwai 6 52:42 4.88%
>> postgres
>>>>>> 1863 pgsql 1 25 0 67542M 388M semwai 25 9:12 2.20%
>> postgres
>>>>>> 1859 pgsql 1 22 0 67538M 1453M *vm ob 20 6:13 2.10%
>> postgres
>>>>>> 1860 pgsql 1 22 0 67538M 1454M sbwait 8 6:08 1.95% postgres
>>>>>> 1848 pgsql 1 21 0 67586M 66676M *vm ob 30 517:07 1.66%
>>>> postgres
>>>>>> 1856 pgsql 1 22 0 67538M 290M *vm ob 15 5:39 1.66%
>> postgres
>>>>>> 1846 pgsql 1 21 0 67538M 163M sbwait 15 5:46 1.46% postgres
>>>>>> 1853 pgsql 1 21 0 67538M 110M sbwait 30 8:54 1.17% postgres
>>>>>> 1989 pgsql 1 23 0 67536M 5180K sbwait 18 1:41 0.98% postgres
>>>>>> 5 root 1 -16 - 0K 16K psleep 6 9:33 0.78% pagedaemon
>>>>>> 1854 pgsql 1 20 0 67538M 338M sbwait 22 5:38 0.78% postgres
>>>>>> 1861 pgsql 1 20 0 67538M 286M sbwait 15 6:13 0.68% postgres
>>>>>> 1857 pgsql 1 20 0 67538M 1454M semwai 10 6:19 0.49%
>> postgres
>>>>>> 1999 pgsql 1 36 0 67538M 156M *vm ob 28 120:56 0.39%
>> postgres
>>>>>> 1851 pgsql 1 20 0 67538M 136M sbwait 22 5:48 0.39% postgres
>>>>>> 1975 pgsql 1 20 0 67536M 5688K sbwait 25 1:40 0.29% postgres
>>>>>> 1858 pgsql 1 20 0 67538M 417M sbwait 3 5:55 0.20% postgres
>>>>>> 2031 pgsql 1 20 0 67536M 5664K sbwait 5 3:26 0.10% postgres
>>>>>> 1834 root 12 20 0 71892K 12848K select 20 34:05 0.00% slon
>>>>>> 12 root 78 -76 - 0K 1248K WAIT 0 25:47 0.00% intr
>>>>>> 2041 pgsql 1 20 0 67536M 5932K sbwait 14 12:50 0.00%
>> postgres
>>>>>> 2039 pgsql 1 20 0 67536M 5960K sbwait 17 9:59 0.00% postgres
>>>>>> 2038 pgsql 1 20 0 67536M 5956K sbwait 6 8:21 0.00% postgres
>>>>>> 2040 pgsql 1 20 0 67536M 5996K sbwait 7 8:20 0.00% postgres
>>>>>> 2032 pgsql 1 20 0 67536M 5800K sbwait 22 7:03 0.00% postgres
>>>>>> 2036 pgsql 1 20 0 67536M 5748K sbwait 23 6:38 0.00% postgres
>>>>>> 1812 pgsql 1 20 0 67538M 59185M select 1 5:46 0.00% postgres
>>>>>> 2005 pgsql 1 20 0 67536M 5788K sbwait 23 5:14 0.00% postgres
>>>>>> 2035 pgsql 1 20 0 67536M 4892K sbwait 18 4:52 0.00%
>> <postgres>
>>>>>> 1852 pgsql 1 21 0 67536M 1230M semwai 7 4:47 0.00%
>> postgres
>>>>>> 13 root 3 -8 - 0K 48K - 28 4:46 0.00% geom
>>>>>>
>>>>>>
>>>>> Another thing I've noticed is that this sysctl vm.stats counter is
>> increasing
>>>> fairly rapidly:
>>>>> # sysctl vm.stats.vm.v_pdpages && sleep 1 && sysctl
>>>> vm.stats.vm.v_pdpages
>>>>> vm.stats.vm.v_pdpages: 3455264541
>>>>> vm.stats.vm.v_pdpages: 3662158383
>>>> I'm not sure what that tells us, because both the page daemon and the
>> vm
>>>> ("swap") daemon increment this counter.
>>>>
>>>>> Also, to demonstrate what kind of problems this seems to cause:
>>>>> # time sleep 1
>>>>>
>>>>> real 0m18.288s
>>>>> user 0m0.001s
>>>>> sys 0m0.004s
>>>> If you change the sysctl vm.swap_enabled to 0, how does your system
>>>> behave?
>>>>
>>> Setting vm.swap_enabled to 0 made the problem clear up almost
>> instantly. vmdaemon is back to 0.00% CPU usage and the system is
>> responsive once again.
>>>
>> I doubt that you need whole process swapping. The page daemon is
>> probably sufficient. See how things go for a few days and let me know.
>>
>> There is still a bug here that needs diagnosing and fixing. So, I will
>> likely send you a debugging patch in the near future, and ask you to
>> reenable swapping under that patch.
>>
> If it helps at all - setting vm.swap_enabled=0 seems to fix the problem even without the aforementioned patch to vm_pageout.c.
>
Nonetheless, I would recommend that you deploy that patch.
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