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

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Message-ID: <CAHk-=wiEUPBzAOPkH1aHypnxW6+vVtmCw_vsOPgNZtOvQnrG8w@mail.gmail.com>
Date:   Tue, 27 Nov 2018 14:50:05 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     rong.a.chen@...el.com, Michal Hocko <mhocko@...e.com>,
        s.priebe@...fihost.ag, alex.williamson@...hat.com,
        mgorman@...hsingularity.net, zi.yan@...rutgers.edu,
        Vlastimil Babka <vbabka@...e.cz>, rientjes@...gle.com,
        kirill@...temov.name, Andrew Morton <akpm@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        lkp@...org
Subject: Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression

On Tue, Nov 27, 2018 at 12:57 PM Andrea Arcangeli <aarcange@...hat.com> wrote:
>
> This difference can only happen with defrag=always, and that's not the
> current upstream default.

Ok, thanks. That makes it a bit less critical.

> That MADV_HUGEPAGE causes flights with NUMA balancing is not great
> indeed, qemu needs NUMA locality too, but then the badness caused by
> __GFP_THISNODE was a larger regression in the worst case for qemu.
[...]
> So the short term alternative again would be the alternate patch that
> does __GFP_THISNODE|GFP_ONLY_COMPACT appended below.

Sounds like we should probably do this. Particularly since Vlastimil
pointed out that we'd otherwise have issues with the back-port for 4.4
where that "defrag=always" was the default.

The patch doesn't look horrible, and it directly addresses this
particular issue.

Is there some reason we wouldn't want to do it?

               Linus