linux-kernel - Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression

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Date:   Wed, 5 Dec 2018 14:12:35 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Andrea Arcangeli <aarcange@...hat.com>,
        mgorman@...hsingularity.net, Vlastimil Babka <vbabka@...e.cz>,
        mhocko@...nel.org, ying.huang@...el.com, s.priebe@...fihost.ag,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        alex.williamson@...hat.com, lkp@...org, kirill@...temov.name,
        Andrew Morton <akpm@...ux-foundation.org>,
        zi.yan@...rutgers.edu
Subject: Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3%
 regression

On Wed, 5 Dec 2018, Linus Torvalds 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.
> 

Please allow me to prepare my v2 because it's not a clean revert due to 
the follow-up 89c83fb539f9 ("mm, thp: consolidate THP gfp handling into 
alloc_hugepage_direct_gfpmask") and will incorporate the feedback from 
Michal to not change anything outside of the thp fault path.