Re: [LKP] [lkp-robot] [mm, memcontrol] 309fe96bfc: vm-scalability.throughput +23.0% improvement

Michal Hocko
2018-05-29T07:58:04Z

On Tue 29-05-18 03:15:51, Lu, Aaron wrote:
> On Mon, 2018-05-28 at 14:03 +0200, Michal Hocko wrote:
> > On Mon 28-05-18 19:40:19, kernel test robot wrote:
> > >
> > > Greeting,
> > >
> > > FYI, we noticed a +23.0% improvement of vm-scalability.throughput due to commit:
> > >
> > >
> > > commit: 309fe96bfc0ae387f53612927a8f0dc3eb056efd ("mm, memcontrol: implement memory.swap.events")
> > > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
> >
> > This doesn't make any sense to me. The patch merely adds an accounting.
> > It doesn't optimize anything. So I strongly suspect the result is just
> > misleading or the test (environment) misconfigured. Not the first time
> > I am seeing something like that I am afraid.
> >
>
> Most likely the same situation as:
> "
> FYI, we noticed a -27.2% regression of will-it-scale.per_process_ops
> due to commit:
>
>
> commit: e27be240df53f1a20c659168e722b5d9f16cc7f4 ("mm: memcg: make sure
> memory.events is uptodate when waking pollers")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> "
>
> Where the performance change is due to layout change of
> 'struct mem_cgroup':
> http://lkml.kernel.org/r/20180528085201.GA2918@intel.com

I do not follow. How can _this_ patch lead to an improvement when it
actually _adds_ an accounting? The other report you are mentioning is a
_regression_ and I can imagine that the layout changes can lead to that
result.
--
Michal Hocko
SUSE Labs