linux-kernel - Re: [patch 0/8] mm: thrash detection-based file cache sizing v5

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Message-ID: <20131022093512.GC707@cmpxchg.org>
Date:	Tue, 22 Oct 2013 05:35:12 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Greg Thelen <gthelen@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan.kim@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Michel Lespinasse <walken@...gle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Roman Gushchin <klamm@...dex-team.ru>,
	Ozgun Erdogan <ozgun@...usdata.com>,
	Metin Doslu <metin@...usdata.com>, Tejun Heo <tj@...nel.org>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 0/8] mm: thrash detection-based file cache sizing v5

On Mon, Oct 21, 2013 at 11:26:43AM +0200, Vlastimil Babka wrote:
> On 10/10/2013 11:46 PM, Johannes Weiner wrote:
> > Hi everyone,
> > 
> > here is an update to the cache sizing patches for 3.13.
> > 
> > 	Changes in this revision
> > 
> > o Drop frequency synchronization between refaulted and demoted pages
> >   and just straight up activate refaulting pages whose access
> >   frequency indicates they could stay in memory.  This was suggested
> >   by Rik van Riel a looong time ago but misinterpretation of test
> >   results during early stages of development took me a while to
> >   overcome.  It's still the same overall concept, but a little simpler
> >   and with even faster cache adaptation.  Yay!
> 
> Oh, I liked the previous approach with direct competition between the
> refaulted and demoted page :) Doesn't the new approach favor the
> refaulted page too much? No wonder it leads to faster cache adaptation,
> but could it also cause degradations for workloads that don't benefit
> from it? Were there any tests for performance regressions on workloads
> that were not the target of the patchset?

If anything, it's unfair to refaulting pages because it requires 3
references before they are activated instead of the regular 2.

We don't do the direct competition for regular in-core activation,
either, which has the same theoretical problem but was never an issue
in the real world.  Not that I know of anyway.

I ran a standard battery of mmtests (kernbench, dbench, postmark,
micro, fsmark, what have you) and did not notice any regressions.
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