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

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Date:	Thu, 14 Nov 2013 10:56:32 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Vlastimil Babka <vbabka@...e.cz>
CC:	Johannes Weiner <hannes@...xchg.org>,
	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>,
	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 10/21/2013 05:26 AM, 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?

This is a good question, and one that is probably
best settled through experimentation.

Even with the first scheme (fault refaulted page to
the inactive list), those pages only need 2 accesses
to be promoted to the active list.

That is because a refault tends to immediately be
followed by an access (after all, the attempted
access causes the page to get loaded back into memory).
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