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

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Message-ID: <20181203185954.GM31738@dhcp22.suse.cz>
Date:   Mon, 3 Dec 2018 19:59:54 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     ying.huang@...el.com, Andrea Arcangeli <aarcange@...hat.com>,
        s.priebe@...fihost.ag, mgorman@...hsingularity.net,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        alex.williamson@...hat.com, lkp@...org,
        David Rientjes <rientjes@...gle.com>, kirill@...temov.name,
        Andrew Morton <akpm@...ux-foundation.org>,
        zi.yan@...rutgers.edu, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3%
 regression

On Mon 03-12-18 10:45:35, Linus Torvalds wrote:
> On Mon, Dec 3, 2018 at 10:30 AM Michal Hocko <mhocko@...nel.org> wrote:
> >
> > I do not get it. 5265047ac301 which this patch effectively reverts has
> > regressed kvm workloads. People started to notice only later because
> > they were not running on kernels with that commit until later. We have
> > 4.4 based kernels reports. What do you propose to do for those people?
> 
> We have at least two patches that others claim to fix things.
> 
> You dismissed them and said "can't be done".

You are misinterpreting my words. I haven't dismissed anything. I do
recognize both usecases under discussion.

I have merely said that a better THP locality needs more work and during
the review discussion I have even volunteered to work on that. There
are other reclaim related fixes under work right now. All I am saying
is that MADV_TRANSHUGE having numa locality implications cannot satisfy
all the usecases and it is particurarly KVM that suffers from it.
-- 
Michal Hocko
SUSE Labs