linux-kernel - Re: [LKP] [lkp] [xfs] 68a9f5e700: aim7.jobs-per-min -13.6% regression

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Date:	Wed, 17 Aug 2016 18:42:54 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mel Gorman <mgorman@...hsingularity.net>,
	Minchan Kim <minchan@...nel.org>,
	Vladimir Davydov <vdavydov@...tuozzo.com>,
	Dave Chinner <david@...morbit.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bob Peterson <rpeterso@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	Christoph Hellwig <hch@....de>,
	Wu Fengguang <fengguang.wu@...el.com>, LKP <lkp@...org>,
	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [LKP] [lkp] [xfs] 68a9f5e700: aim7.jobs-per-min -13.6% regression

On Wed 17-08-16 17:48:25, Michal Hocko wrote:
[...]
> I will try to catch up with the rest of the email thread but from a
> quick glance it just feels like we are doing more more work under the
> lock.

Hmm, so it doesn't seem to be more work in __remove_mapping as pointed
out in http://lkml.kernel.org/r/20160816220250.GI16044@dastard

As Mel already pointed out the LRU will be basically single mapping for
this workload so any subtle change in timing might make a difference.
I was looking through 4.6..4.7 and one thing that has changed is the
inactive vs. active LRU size ratio. See 59dc76b0d4df ("mm: vmscan:
reduce size of inactive file list"). The machine has quite a lot of
memory and so the LRUs will be large as well so I guess this could have
change the timing somehow, but it feels like a wild guess so I would be
careful to blame this commit...
-- 
Michal Hocko
SUSE Labs