linux-kernel - Re: [LKP] [lkp] [mm, oom] faad2185f4: vm-scalability.throughput -11.8% regression

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Date:	Thu, 28 Apr 2016 13:21:35 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Aaron Lu <aaron.lu@...el.com>
Cc:	"Huang, Ying" <ying.huang@...el.com>,
	kernel test robot <xiaolong.ye@...el.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, lkp@...org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org
Subject: Re: [LKP] [lkp] [mm, oom] faad2185f4: vm-scalability.throughput
 -11.8% regression

On Thu 28-04-16 17:45:23, Aaron Lu wrote:
> On 04/28/2016 04:57 PM, Michal Hocko wrote:
> > On Thu 28-04-16 13:17:08, Aaron Lu wrote:
[...]
> >> I have the same doubt too, but the results look really stable(only for
> >> commit 0da9597ac9c0, see below for more explanation).
> > 
> > I cannot seem to find this sha1. Where does it come from? linux-next?
> 
> Neither can I...
> The commit should come from 0day Kbuild service I suppose, which is a
> robot to do automatic fetch/building etc.
> Could it be that the commit appeared in linux-next some day and then
> gone?

This wouldn't be unusual because mmotm part of the linux next is
constantly rebased.

[...]
> > OK, so we have 96G for consumers with 32G RAM and 96G of swap space,
> > right?  That would suggest they should fit in although the swapout could
> > be large (2/3 of the faulted memory) and the random pattern can cause
> > some trashing. Does the system bahave the same way with the stream anon
> > load? Anyway I think we should be able to handle such load, although it
> 
> By stream anon load, do you mean continuous write, without read?

Yes

> > is quite untypical from my experience because it can be pain with a slow
> > swap but ramdisk swap should be as fast as it can get so the swap in/out
> > should be basically noop. 
> > 
> >> So I guess the question here is, after the OOM rework, is the OOM
> >> expected for such a case? If so, then we can ignore this report.
> > 
> > Could you post the OOM reports please? I will try to emulate a similar
> > load here as well.
> 
> I attached the dmesg from one of the runs.
[...]
> [   77.434044] slabinfo invoked oom-killer: gfp_mask=0x26040c0(GFP_KERNEL|__GFP_COMP|__GFP_NOTRACK), order=2, oom_score_adj=0
[...]
> [  138.090480] kthreadd invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
[...]
> [  141.823925] lkp-setup-rootf invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0

All of them are order-2 and this was a known problem for "mm, oom:
rework oom detection" commit and later should make it much more
resistant to failures for higher (!costly) orders. So I would definitely
encourage you to retest with the current _complete_ mmotm tree.
-- 
Michal Hocko
SUSE Labs