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

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Message-ID: <22f6781b-9cc4-4857-b3e1-e2d9f595f64d@default>
Date:	Thu, 26 Jan 2012 21:15:16 -0800 (PST)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Rik van Riel <riel@...hat.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)

> From: Rik van Riel [mailto:riel@...hat.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...

I suspected that was true, but was just brainstorming.
Thanks for confirming.

Are there any other page bits that are dont-care when
a page is on an LRU list?

I'd also be interested in your/RedHat's opinion on the
64-bit vs 32-bit market.  Will RHEL7 even support 32-bit?

Dan

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