linux-kernel - Re: [PATCH] mm: implement WasActive page flag (for improving cleancache)

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Message-ID: <4F221AFE.6070108@redhat.com>
Date:	Thu, 26 Jan 2012 22:33:18 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Konrad Wilk <konrad.wilk@...cle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>,
	Nebojsa Trpkovic <trx.lists@...il.com>, minchan@...nel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Chris Mason <chris.mason@...cle.com>
Subject: Re: [PATCH] mm: implement WasActive page flag (for improving cleancache)

On 01/26/2012 09:43 PM, Dan Magenheimer wrote:

> Maybe the Active page bit could be overloaded with some minor
> rewriting?  IOW, perhaps the Active bit could be ignored when
> the page is moved to the inactive LRU?  (Confusing I know, but I am
> just brainstorming...)

The PG_referenced bit is already overloaded.  We keep
the bit set when we move a page from the active to the
inactive list, so a page that was previously active
only needs to be referenced once to become active again.

The LRU bits (PG_lru, PG_active, etc) are needed to
figure out which LRU list the page is on.  I don't
think we can overload those...

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