[ovirt-users] VDSM memory consumption

[Dan Kenigsberg]

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.