[ovs-discuss] ovs-vswitchd process huge memory consumption

Thu Mar 7 07:54:42 UTC 2019

On Wed, Mar 6, 2019 at 7:01 PM Oleg Bondarev <obondarev at mirantis.com> wrote:

>
> I'm thinking if this can be malloc() not returning memory to the system
> after peak loads:
> *"Occasionally, free can actually return memory to the operating system
> and make the process smaller. Usually, all it can do is allow a later call
> to malloc to reuse the space. In the meantime, the space remains in your
> program as part of a free-list used internally by malloc." [1]*
>
> Does it sound sane? If yes, what would be a best way to check that?
>

Seems that's not the case. On one of the nodes memory usage by ovs-vswitchd
grew from 84G to 87G for the past week, and on other nodes grows gradually
as well.

>
> [1] http://www.gnu.org/software/libc/manual/pdf/libc.pdf
>
> Thanks,
> Oleg
>
> On Wed, Mar 6, 2019 at 12:34 PM Oleg Bondarev <obondarev at mirantis.com>
> wrote:
>
>> Hi,
>>
>> On Wed, Mar 6, 2019 at 1:08 AM Ben Pfaff <blp at ovn.org> wrote:
>>
>>> Starting from 0x30, this looks like a "minimatch" data structure, which
>>> is a kind of compressed bitwise match against a flow.
>>>
>>> 00000030: 0000 0000 0000 4014 0000 0000 0000 0000
>>> 00000040: 0000 0000 0000 0000 fa16 3e2b c5d5 0000 0000 0022 0000 0000
>>>
>>> 00000058: 0000 0000 0000 4014 0000 0000 0000 0000
>>> 00000068: 0000 0000 ffff ffff ffff ffff ffff 0000 0000 0fff 0000 0000
>>>
>>> I think this corresponds to a flow of this form:
>>>
>>>
>>> pkt_mark=0xc5d5/0xffff,skb_priority=0x3e2bfa16,reg13=0,mpls_label=2,mpls_tc=1,mpls_ttl=0,mpls_bos=0
>>>
>>> Is that at all meaningful?  Does it match anything that appears in the
>>> OpenFlow flow table?
>>>
>>
>> Not sure, actually fa:16:3e:2b:c5:d5 is a mac address of a neutron port
>> (this is an OpenStack cluster) - the port is a VM port.
>> fa:16:3e/fa:16:3f - are standard neutron mac prefixes. That makes me
>> think those might be some actual eth packets (broadcasts?) that somehow
>> stuck in memory..
>> So I didn't find anything similar in the flow tables. I'm attaching flows
>> of all 5 OVS bridges on the node.
>>
>>
>>>
>>> Are you using the kernel or DPDK datapath?
>>>
>>
>> It's kernel datapath, no DPDK. Ubuntu with 4.13.0-45  kernel.
>>
>>
>>>
>>> On Tue, Mar 05, 2019 at 08:42:14PM +0400, Oleg Bondarev wrote:
>>> > Hi,
>>> >
>>> > thanks for your help!
>>> >
>>> > On Tue, Mar 5, 2019 at 7:26 PM Ben Pfaff <blp at ovn.org> wrote:
>>> >
>>> > > You're talking about the email where you dumped out a repeating
>>> sequence
>>> > > from some blocks?  That might be the root of the problem, if you can
>>> > > provide some more context.  I didn't see from the message where you
>>> > > found the sequence (was it just at the beginning of each of the 4 MB
>>> > > blocks you reported separately, or somewhere else), how many copies
>>> of
>>> > > it, or if you were able to figure out how long each of the blocks
>>> was.
>>> > > If you can provide that information I might be able to learn some
>>> > > things.
>>> > >
>>> >
>>> > Yes, those were beginnings of 0x4000000 size blocks reported by the
>>> script.
>>> > I also checked 0x8000000 blocks reported and the content is the same.
>>> > Examples of how those blocks end:
>>> >  - https://pastebin.com/D9M6T2BA
>>> >  - https://pastebin.com/gNT7XEGn
>>> >  - https://pastebin.com/fqy4XDbN
>>> >
>>> > So basically contents of the blocks are sequences of:
>>> >
>>> > *00000020: 0000 0000 0000 0000 6500 0000 0000 0000  ........e.......*
>>> > *00000030: 0000 0000 0000 4014 0000 0000 0000 0000  ...... at .........*
>>> > *00000040: 0000 0000 0000 0000 fa16 3e2b c5d5 0000  ..........>+....*
>>> > *00000050: 0000 0022 0000 0000 0000 0000 0000 4014  ...".......... at .*
>>> > *00000060: 0000 0000 0000 0000 0000 0000 ffff ffff  ................*
>>> > *00000070: ffff ffff ffff 0000 0000 0fff 0000 0000  ................*
>>> >
>>> > following each other and sometimes separated by sequences like this:
>>> >
>>> > *00001040: 6861 6e64 6c65 7232 3537 0000 0000 0000  handler257......*
>>> >
>>> > I ran the scripts against several core dumps of several compute nodes
>>> with
>>> > the issue and
>>> > the picture is pretty much the same: 0x4000000 blocks and less
>>> 0x8000000
>>> > blocks.
>>> > I checked the core dump from a compute node where OVS memory
>>> consumption
>>> > was ok:
>>> > no such block sizes reported.
>>> >
>>> >
>>> > >
>>> > > On Tue, Mar 05, 2019 at 09:07:55AM +0400, Oleg Bondarev wrote:
>>> > > > Hi Ben,
>>> > > >
>>> > > > I didn't have a chance to debug the scripts yet, but just in case
>>> you
>>> > > > missed my last email with examples of repeatable blocks
>>> > > > and sequences - do you think we still need to analyze further,
>>> will the
>>> > > > scripts tell more about the heap?
>>> > > >
>>> > > > Thanks,
>>> > > > Oleg
>>> > > >
>>> > > > On Thu, Feb 28, 2019 at 10:14 PM Ben Pfaff <blp at ovn.org> wrote:
>>> > > >
>>> > > > > On Tue, Feb 26, 2019 at 01:41:45PM +0400, Oleg Bondarev wrote:
>>> > > > > > Hi,
>>> > > > > >
>>> > > > > > thanks for the scripts, so here's the output for a 24G core
>>> dump:
>>> > > > > > https://pastebin.com/hWa3R9Fx
>>> > > > > > there's 271 entries of 4MB - does it seem something we should
>>> take a
>>> > > > > closer
>>> > > > > > look at?
>>> > > > >
>>> > > > > I think that this output really just indicates that the script
>>> failed.
>>> > > > > It analyzed a lot of regions but didn't output anything useful.
>>> If it
>>> > > > > had worked properly, it would have told us a lot about data
>>> blocks that
>>> > > > > had been allocated and freed.
>>> > > > >
>>> > > > > The next step would have to be to debug the script.  It
>>> definitely
>>> > > > > worked for me before, because I have fixed at least 3 or 4 bugs
>>> based
>>> > > on
>>> > > > > it, but it also definitely is a quick hack and not something
>>> that I can
>>> > > > > stand behind.  I'm not sure how to debug it at a distance.  It
>>> has a
>>> > > > > large comment that describes what it's trying to do.  Maybe that
>>> would
>>> > > > > help you, if you want to try to debug it yourself.  I guess it's
>>> also
>>> > > > > possible that glibc has changed its malloc implementation; if
>>> so, then
>>> > > > > it would probably be necessary to start over and build a new
>>> script.
>>> > > > >
>>> > >
>>>
>>
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