linux-kernel - Re: [PATCH] mm: page_alloc: High-order per-cpu page allocator v7

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Message-ID: <20161208092231.55c7eacf@redhat.com>
Date:   Thu, 8 Dec 2016 09:22:31 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux-Kernel <linux-kernel@...r.kernel.org>, brouer@...hat.com
Subject: Re: [PATCH] mm: page_alloc: High-order per-cpu page allocator v7

On Wed, 7 Dec 2016 23:25:31 +0000
Mel Gorman <mgorman@...hsingularity.net> wrote:

> On Wed, Dec 07, 2016 at 09:19:58PM +0000, Mel Gorman wrote:
> > At small packet sizes on localhost, I see relatively low page allocator
> > activity except during the socket setup and other unrelated activity
> > (khugepaged, irqbalance, some btrfs stuff) which is curious as it's
> > less clear why the performance was improved in that case. I considered
> > the possibility that it was cache hotness of pages but that's not a
> > good fit. If it was true then the first test would be slow and the rest
> > relatively fast and I'm not seeing that. The other side-effect is that
> > all the high-order pages that are allocated at the start are physically
> > close together but that shouldn't have that big an impact. So for now,
> > the gain is unexplained even though it happens consistently.
> >   
> 
> Further investigation led me to conclude that the netperf automation on
> my side had some methodology errors that could account for an artifically
> low score in some cases. The netperf automation is years old and would
> have been developed against a much older and smaller machine which may be
> why I missed it until I went back looking at exactly what the automation
> was doing. Minimally in a server/client test on remote maching there was
> potentially higher packet loss than is acceptable. This would account why
> some machines "benefitted" while others did not -- there would be boot to
> boot variations that some machines happened to be "lucky". I believe I've
> corrected the errors, discarded all the old data and scheduled a rest to
> see what falls out.

I guess you are talking about setting the netperf socket queue low
(+256 bytes above msg size), that I pointed out in[1].  I can see from
GitHub-mmtests-commit[2] "netperf: Set remote and local socket max
buffer sizes", that you have removed that, good! :-)

>From the same commit[2] I can see you explicitly set (local+remote):

  sysctl net.core.rmem_max=16777216
  sysctl net.core.wmem_max=16777216

Eric do you have any advice on this setting?

And later[4] you further increase this to 32MiB.  Notice that the
netperf UDP_STREAM test will still use the default value from:
net.core.rmem_default = 212992.

(To Eric) Mel's small UDP queues also interacted badly with Eric and
Paolo's UDP improvements, which was fixed in net-next commit[3]
363dc73acacb ("udp: be less conservative with sock rmem accounting").


[1] http://lkml.kernel.org/r/20161201183402.2fbb8c5b@redhat.com
[2] https://github.com/gormanm/mmtests/commit/7f16226577b
[3] https://git.kernel.org/davem/net-next/c/363dc73acacb
[4] https://github.com/gormanm/mmtests/commit/777d1f5cd08
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer