[ovirt-users] VDSM memory consumption

[John Taylor]

Dan Kenigsberg <danken at redhat.com> writes:

> On Sat, Mar 28, 2015 at 10:20:25AM -0400, John Taylor wrote:
>> Daniel Helgenberger <daniel.helgenberger at m-box.de> writes:
>> 
>> > Hello Everyone,
>> >
>> > I did create the original BZ on this. In the mean time, lab system I
>> > used is dismantled and the production system is yet to deploy.
>> >
>> > As I wrote in BZ1147148 [1], I experienced two different issues. One,
>> > one big mem leak of about 15MiB/h and a smaller one, ~300KiB. These seem
>> > unrelated.
>> >
>> > The larger leak was indeed related to SSL in some way; not necessarily
>> > M2Crypto. However, after disabling SSL this was gone leaving the smaller
>> > leak.
>> >
>> > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1147148
>> 
>> 
>> I think there are, at least for the purpose of this discussion, 3 leaks:
>> 1. the M2Crypto leak
>> 2. a slower leak 
>> 3. a large leak that's not M2Crypto related that's part of sampling
>> 
>> My efforts have been around finding the source of my larger leak, which
>> I think is #3.  I had disabled ssl so I knew that M2Crypto
>> isn't/shouldn't be the problem as in bz1147148, and ssl is beside the
>> point as it happens with a deactived host. It's part of sampling which
>> always runs.
>> 
>> What I've found is, after trying to get the smallest reproducer, that
>> it's not the netlink.iter_links that I commented on in [1] that is the
>> problem. But in the _get_intefaces_and_samples loop is the call to
>> create an InterfaceSample and that has getLinkSpeed() which, for vlans,
>> ends up calling ipwrapper.getLink, and that to
>> netlink.get_link(name)
>> 
>> netlink.get_link(name) *is* the source of my big leak. This is vdsm
>> 4.16.10, so it is [2] and it's been changed in master for the removal of
>> support for libnl v1 so it might not be a problem anymore. 
>>  
>> def get_link(name):
>>     """Returns the information dictionary of the name specified link."""
>>     with _pool.socket() as sock:
>>         with _nl_link_cache(sock) as cache:
>>             link = _rtnl_link_get_by_name(cache, name)
>>             if not link:
>>                 raise IOError(errno.ENODEV, '%s is not present in the system' %
>>                               name)
>>             return _link_info(cache, link)
>> 
>> 
>> The libnl documentation note at [3] says that for the rtnl_link_get_by_name function 
>> "Attention
>>     The reference counter of the returned link object will be incremented. Use rtnl_link_put() to release the reference."
>> 
>> So I took that hint, and made a change that does the rtnl_link_put() in
>> get_link(name) and it looks like it works for me.
>> 
>> diff oldnetlink.py netlink.py
>> 67d66
>> <             return _link_info(cache, link)
>> 68a68,70
>> >             li = _link_info(cache, link)
>> >             _rtnl_link_put(link)
>> >             return li
>> 333a336,337
>> > 
>> > _rtnl_link_put  = _none_proto(('rtnl_link_put', LIBNL_ROUTE))
>> 
>> Hope that helps. And if someone else could confirm that would be great.
>> 
>> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1158108
>> [2]
>> https://gerrit.ovirt.org/gitweb?p=vdsm.git;a=blob;f=lib/vdsm/netlink.py;h=afae5cecb5ce701d00fb8f019ec92b3331a39036;hb=5608cfdf43db9186dabac4b2a779f9557e798968
>> [3] http://www.infradead.org/~tgr/libnl/doc/api/group__link.html#ga1d583e4f0b43c89d854e5e681a529fad
>
> Thanks, John, for a great detective work.
>
> I'm afraid that with even on the master branch we keep calling
> rtnl_link_get_link() and rtnl_link_get_by_name() without clearing the
> reference count, so a fix is due there, too.
>
> Would you consider posting a fully-fledged fix to gerrit? I still need
> to understand what is the use of that refcount, so that we do not
> release it too early.
>
> Regards,
> Dan.

Dan,

I'm happy to [1], although I've probably gotten something wrong with how
it's supposed to be done :) It's for the version I'm using so it's for
branch ovirt-3.5.

[1] https://gerrit.ovirt.org/#/c/39372/

Thanks,
-John