linux-kernel - Re: [lkp] [mm] 795ae7a0de: pixz.throughput -9.1% regression

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Message-ID: <20160603090046.GF2469@suse.de>
Date:	Fri, 3 Jun 2016 10:00:46 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	kernel test robot <xiaolong.ye@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org
Subject: Re: [lkp] [mm] 795ae7a0de: pixz.throughput -9.1% regression

On Thu, Jun 02, 2016 at 12:07:06PM -0400, Johannes Weiner wrote:
> right before the test is running? I wonder if it's mostly filled with
> cache, and the increase in watermarks causes a higher portion of the
> anon allocs and frees to spill to the remote node, but never enough to
> enter the allocator slowpath and waking kswapd to fix it.
> 
> Another suspect is the fair zone allocator, whose allocation batches
> increased as well. It shouldn't affect NUMA placement, but I wonder if
> there is a bug in there that causes false spilling to foreign nodes
> that was only bounded by the allocation batch of the foreign zone.
> Mel, does such a symptom sound familiar in any way?
> 

Unfortunately not. The closest I've seen recently is bugs in the page
allocator patches that artifically enters the slow path prematurely but
that does not appear to apply here.

-- 
Mel Gorman
SUSE Labs