linux-kernel - Re: [rfc 2/3] mm: vmscan: treat inactive cycling as neutral

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Message-Id: <20111107113417.1b7581a5.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 7 Nov 2011 11:34:17 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Johannes Weiner <jweiner@...hat.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...allels.com>,
	Pekka Enberg <penberg@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Minchan Kim <minchan.kim@...il.com>,
	Gene Heskett <gene.heskett@...il.com>
Subject: Re: [rfc 2/3] mm: vmscan: treat inactive cycling as neutral

On Wed, 2 Nov 2011 17:32:13 +0100
Johannes Weiner <jweiner@...hat.com> wrote:

> Each page that is scanned but put back to the inactive list is counted
> as a successful reclaim, which tips the balance between file and anon
> lists more towards the cycling list.
> 
> This does - in my opinion - not make too much sense, but at the same
> time it was not much of a problem, as the conditions that lead to an
> inactive list cycle were mostly temporary - locked page, concurrent
> page table changes, backing device congested - or at least limited to
> a single reclaimer that was not allowed to unmap or meddle with IO.
> More important than being moderately rare, those conditions should
> apply to both anon and mapped file pages equally and balance out in
> the end.
> 
> Recently, we started cycling file pages in particular on the inactive
> list much more aggressively, for used-once detection of mapped pages,
> and when avoiding writeback from direct reclaim.
> 
> Those rotated pages do not exactly speak for the reclaimability of the
> list they sit on and we risk putting immense pressure on file list for
> no good reason.
> 
> Instead, count each page not reclaimed and put back to any list,
> active or inactive, as rotated, so they are neutral with respect to
> the scan/rotate ratio of the list class, as they should be.
> 
> Signed-off-by: Johannes Weiner <jweiner@...hat.com>

I think this makes sense.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

I wonder it may be better to have victim list for written-backed pages..

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