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

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Date:   Tue, 29 May 2018 09:58:00 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Lu, Aaron" <aaron.lu@...el.com>
Cc:     "Ye, Xiaolong" <xiaolong.ye@...el.com>,
        "tj@...nel.org" <tj@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lkp@...org" <lkp@...org>,
        "hannes@...xchg.org" <hannes@...xchg.org>
Subject: Re: [LKP] [lkp-robot] [mm, memcontrol] 309fe96bfc:
 vm-scalability.throughput +23.0% improvement

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