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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 5 Dec 2018 14:03:10 -0800
Message-ID: <CAHk-=whi8Ju-cTDL4cYtwuLA7BYgGJYyy6HVMoknZaLHnRc83g@mail.gmail.com>
Subject: Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression
To:     Andrea Arcangeli <aarcange@redhat.com>
Cc:     mgorman@techsingularity.net, Vlastimil Babka <vbabka@suse.cz>,
        mhocko@kernel.org, ying.huang@intel.com, s.priebe@profihost.ag,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        alex.williamson@redhat.com, lkp@01.org,
        David Rientjes <rientjes@google.com>, kirill@shutemov.name,
        Andrew Morton <akpm@linux-foundation.org>,
        zi.yan@cs.rutgers.edu
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On Wed, Dec 5, 2018 at 12:40 PM Andrea Arcangeli <aarcange@redhat.com> wrote:
>
> So ultimately we decided that the saner behavior that gives the least
> risk of regression for the short term, until we can do something
> better, was the one that is already applied upstream.

You're ignoring the fact that people *did* report things regressed.

That's the part I find unacceptable. You're saying "we picked
something that minimized regressions".

No it didn't. The regression is present and real, and is on a real
load, not a benchmark.

So that argument is clearly bogus.

I'm going to revert the commit since people apparently seem to be
ignoring this fundamental issue.

Real workloads regressed.  The regressions got reported. Ignoring that
isn't acceptable.

                    Linus