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Date:   Tue, 21 May 2019 11:13:55 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     kernel test robot <rong.a.chen@intel.com>
Cc:     lkp@01.org, LKML <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Shakeel Butt <shakeelb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>
Subject: Re: [LKP] [mm] 42a3003535: will-it-scale.per_process_ops -25.9%
 regression
Message-ID: <20190521151355.GA2870@cmpxchg.org>
References: <20190520063534.GB19312@shao2-debian>
 <20190520215328.GA1186@cmpxchg.org>
 <20190521134646.GE19312@shao2-debian>
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On Tue, May 21, 2019 at 09:46:46PM +0800, kernel test robot wrote:
> On Mon, May 20, 2019 at 05:53:28PM -0400, Johannes Weiner wrote:
> > Hello,
> > 
> > On Mon, May 20, 2019 at 02:35:34PM +0800, kernel test robot wrote:
> > > Greeting,
> > > 
> > > FYI, we noticed a -25.9% regression of will-it-scale.per_process_ops due to commit:
> > > 
> > > 
> > > commit: 42a300353577ccc17ecc627b8570a89fa1678bec ("mm: memcontrol: fix recursive statistics correctness & scalabilty")
> > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> > > 
> > > in testcase: will-it-scale
> > > on test machine: 192 threads Skylake-SP with 256G memory
> > > with following parameters:
> > 
> > Ouch. That has to be the additional cache footprint of the split
> > local/recursive stat counters, rather than the extra instructions.
> > 
> > Could you please try re-running the test on that host with the below
> > patch applied?
> 
> Hi,
> 
> The patch can fix the regression.
> 
> tests: 1
> testcase/path_params/tbox_group/run: will-it-scale/performance-process-100%-page_fault3/lkp-skl-4sp1
> 
> db9adbcbe7 ("mm: memcontrol: move stat/event counting functions out-of-line")
> 8d8245997d ("mm: memcontrol: don't batch updates of local VM stats and events")
> 
> db9adbcbe740e098  8d8245997dbd17c5056094f15c  
> ----------------  --------------------------  
>          %stddev      change         %stddev
>              \          |                \  
>   87819982                    85307742        will-it-scale.workload
>     457395                      444310        will-it-scale.per_process_ops

Fantastic, thank you for verifying! I'm going to take that as a
Tested-by.